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# State Management Standards for Vitest This document outlines the coding standards for state management when writing tests with Vitest, the next-gen testing framework powered by Vite. It aims to guide developers in creating robust, maintainable, and performant tests by adopting modern best practices for managing application state, data flow, and reactivity within the testing context. ## 1. Introduction to State Management in Vitest While Vitest primarily focuses on unit and integration testing, understanding state management principles is crucial for creating effective and reliable tests, especially when dealing with complex components or application logic. State might refer to various entities: component internal state, data fetched from external sources, or the overall application state managed by tools like Vuex, Redux, or Pinia. ### 1.1. Why State Management Matters in Testing * **Reproducibility:** Clearly defined state makes tests reproducible, ensuring that failures always indicate real issues. * **Isolation:** Proper state isolation prevents tests from interfering with each other, avoiding flaky test suites. * **Maintainability:** Well-structured state management simplifies test setup and teardown, making tests easier to understand and maintain. * **Accuracy:** Accurate state representation guarantees that tests accurately reflect the actual application behavior. ### 1.2. Scope of these Standards These standards cover: * Approaches for setting up and managing state within tests. * Strategies for isolating state between tests. * Best practices for mocking and stubbing external dependencies that influence state. * Specific considerations for testing reactive state with frameworks like Vue, React, and Svelte. ## 2. General Principles for State Management in Vitest ### 2.1. Declarative vs. Imperative State Setup * **Do This:** Prefer declarative state setup using "beforeEach" or "beforeAll" hooks to define the initial state for each test or test suite. """typescript import { beforeEach, describe, expect, it } from 'vitest'; describe('Counter component', () => { let counter: { value: number }; beforeEach(() => { counter = { value: 0 }; // Declarative state setup }); it('should increment the counter value', () => { counter.value++; expect(counter.value).toBe(1); }); }); """ * **Don't Do This:** Avoid directly modifying the state within the test body unless it's the action being tested. This makes the test harder to read and understand as the initial state becomes implicit. ### 2.2. Isolate State Between Tests * **Do This:** Use "beforeEach" to reset the state before each test, ensuring that tests do not interfere with each other. Consider using a factory function to create fresh state instances. """typescript import { beforeEach, describe, expect, it } from 'vitest'; // Factory function to create a new state object const createCounter = () => ({ value: 0 }); describe('Counter component', () => { let counter: { value: number }; beforeEach(() => { counter = createCounter(); // Creates a fresh counter object for each test }); it('should increment the counter value', () => { counter.value++; expect(counter.value).toBe(1); }); it('should not be affected by previous test', () => { expect(counter.value).toBe(0); // Reset to initial state }); }); """ * **Don't Do This:** Share mutable state directly between tests without resetting it. This can lead to unexpected test failures and makes debugging difficult. ### 2.3. Minimize Global State * **Do This:** Encapsulate the state as much as possible within the component or module being tested. Use dependency injection to provide state dependencies. * **Don't Do This:** Rely heavily on global variables or shared mutable objects to manage state. This introduces tight coupling and makes tests harder to isolate. ### 2.4. Use Mocks and Stubs for External Dependencies * **Do This:** Use "vi.mock" or manual mocks to isolate the component being tested from external dependencies (e.g., databases, APIs). This allows you to control the state returned by the dependencies and focus on testing the component's logic. """typescript // api.ts const fetchData = async () => { const response = await fetch('/api/data'); return await response.json(); }; export default fetchData; // component.test.ts import { describe, expect, it, vi } from 'vitest'; import fetchData from '../api'; // Import the original module import MyComponent from '../MyComponent.vue'; //Example using Vue - framework agnostic principle vi.mock('../api', () => ({ //Mock the whole module default: vi.fn(() => Promise.resolve({ data: 'mocked data' })), })); describe('MyComponent', () => { it('should display mocked data', async () => { const wrapper = mount(MyComponent); await vi.waitFor(() => { // Adjust timeout as needed expect(wrapper.text()).toContain('mocked data'); }); expect(fetchData).toHaveBeenCalled(); }); }); """ * **Don't Do This:** Make real API calls or database queries during tests. This can make tests slow, unreliable, and dependent on external factors. Also avoid tightly coupling tests to a real database or API. ### 2.5. Understanding "vi.mock" vs. "vi.spyOn" * **"vi.mock":** Replaces an entire module (or specific functions within that module) with a mock implementation. Useful when you need to completely control the behavior of a dependency. Importantly, Vitest hoists the mock to the top of the scope, meaning the mock is defined *before* the actual import. This allows you to mock even before the component is imported. * **"vi.spyOn":** Wraps an existing function (either a function on an object or a directly imported function) and allows you to track its calls, arguments, and return values *without* replacing the original implementation. Useful when you want to assert that a function was called with specific arguments, or a certain number of times. However, "vi.spyOn" works on existing objects/functions and can only be used *after* the object is imported and the function exists. """typescript import {describe, expect, it, vi} from 'vitest'; const myModule = { myFunction: (x: number) => x * 2, }; describe('myFunction', () => { it('should call the function with correct arguments', () => { const spy = vi.spyOn(myModule, 'myFunction'); myModule.myFunction(5); expect(spy).toHaveBeenCalledWith(5); }); it('should return the correct value', () => { const spy = vi.spyOn(myModule, 'myFunction'); spy.mockReturnValue(100); expect(myModule.myFunction(5)).toBe(100); }); }); """ ### 2.6. Async State and "vi.waitFor" * **Do This:** When dealing with asynchronous state updates (e.g., fetching data from an API), use "vi.waitFor" to ensure that the state has been updated before making assertions. This is crucial to prevent race conditions and flaky tests. """typescript import { describe, expect, it, vi } from 'vitest'; describe('Async Component', () => { it('should update state after async operation', async () => { let state = { data: null }; const fetchData = async () => { return new Promise((resolve) => { setTimeout(() => { state.data = 'Async Data'; resolve(state.data); }, 100); }); }; await fetchData(); await vi.waitFor(() => { expect(state.data).toBe('Async Data'); // Assert that the state has been updated }); }); }); """ * **Don't Do This:** Rely on fixed timeouts to wait for asynchronous operations to complete. This can lead to flaky tests if the operation takes longer than expected. Manually trigger the resolve using "mockResolvedValue" when mocking async functions. ### 2.7. Testing Reactivity with Testing Frameworks * **Do This:** Leverage framework-specific testing utilities to properly observe and interact with reactive state. For Vue, use "vue-test-utils", for React, use "@testing-library/react", and so on. These utilities provide methods for triggering state changes and waiting for updates to propagate. **Example (Vue with vue-test-utils):** """typescript import {describe, expect, it} from 'vitest'; import {mount} from '@vue/test-utils'; import { ref } from 'vue'; const MyComponent = { template: '<div>{{ count }}</div>', setup() { const count = ref(0); return { count }; } }; describe('MyComponent', () => { it('should render the correct count', async () => { const wrapper = mount(MyComponent); expect(wrapper.text()).toContain('0'); //Simulate interaction with the component (e.g., by emitting an event) wrapper.vm.count = 5; //Direct state change in a simple example - typically you'd trigger event await wrapper.vm.$nextTick(); //Wait for DOM update expect(wrapper.text()).toContain('5'); }); }); """ * **Don't Do This:** Directly manipulate internal component state without using the testing framework's utilities. This can bypass reactivity mechanisms and lead to incorrect test results. Also it results to fragile tests that are dependent on the internal component implementation. ### 2.8. Immutability Where Possible * **Do This:** Favor immutable data structures and state management techniques where applicable to avoid unintended side effects and simplify reasoning about state changes. Libraries like Immer can be helpful for working with immutable data. * **Don't Do This:** Mutate state directly without considering the consequences for other parts of the application or tests. ### 2.9. Testing State Transitions * **Do This:** Explicitly test all possible state transitions in a component or module. Use "describe" blocks to group tests related to specific state transitions. """typescript import { beforeEach, describe, expect, it } from 'vitest'; describe('Component with State Transitions', () => { let componentState: { isLoading: boolean; data: any; error: any }; beforeEach(() => { componentState = { isLoading: false, data: null, error: null }; }); describe('Initial State', () => { it('should start in the loading state', () => { expect(componentState.isLoading).toBe(false); expect(componentState.data).toBeNull(); expect(componentState.error).toBeNull(); }); }); describe('Loading State', () => { it('should set isLoading to true when fetching data', () => { componentState.isLoading = true; expect(componentState.isLoading).toBe(true); }); }); describe('Success State', () => { it('should set data when data is successfully fetched', () => { const mockData = { name: 'Test Data' }; componentState.data = mockData; componentState.isLoading = false; expect(componentState.data).toEqual(mockData); expect(componentState.isLoading).toBe(false); }); }); describe('Error State', () => { it('should set error when fetching data fails', () => { const mockError = new Error('Failed to fetch data'); componentState.error = mockError; componentState.isLoading = false; expect(componentState.error).toEqual(mockError); expect(componentState.isLoading).toBe(false); }); }); }); """ * **Don't Do This:** Assume that state transitions will work correctly without explicit tests. Missing tests for state transitions are frequently causes of bugs. ## 3. Testing Specific State Management Patterns ### 3.1. Testing Vuex/Pinia Stores * **Do This:** Mock the store's actions, mutations, and getters to isolate the component being tested. Use "createLocalVue" (for Vuex) to create a local Vue instance with the mocked store. For Pinia, mock the store directly using "vi.mock". **Example (Pinia with Vitest):** """typescript import {describe, expect, it, vi} from 'vitest'; import {useMyStore} from '../src/stores/myStore'; //Replace with your actual path vi.mock('../src/stores/myStore', () => { return { useMyStore: vi.fn(() => ({ count: 10, increment: vi.fn(), doubleCount: vi.fn().mockReturnValue(20), })), }; }); describe('Component using Pinia store', () => { it('should display the count from the store', () => { const store = useMyStore(); expect(store.count).toBe(10); }); it('should call the increment action when a button is clicked', () => { const store = useMyStore(); //Simulate user interaction or similar that is expected to call store.increment() // ... expect(store.increment).toHaveBeenCalled(); }); }); """ * **Don't Do This:** Directly interact with the real store during component tests. This can make tests slow, and introduces dependencies between tests, increases complexity. Test the store in a separate test file dedicated to store logic. ### 3.2. Testing Redux Reducers and Actions * **Do This:** Test reducers in isolation by providing them with different actions and verifying that they produce the expected state changes. Test actions by dispatching them and asserting on the side effects (e.g., API calls). """typescript import { describe, expect, it } from 'vitest'; import reducer from './reducer'; import { increment, decrement } from './actions'; describe('Counter Reducer', () => { it('should return the initial state', () => { expect(reducer(undefined, {})).toEqual({ value: 0 }); }); it('should handle INCREMENT', () => { expect(reducer({ value: 0 }, increment())).toEqual({ value: 1 }); }); it('should handle DECREMENT', () => { expect(reducer({ value: 1 }, decrement())).toEqual({ value: 0 }); }); }); """ * **Don't Do This:** Test reducers and actions together in a complex integration test. This makes it harder to isolate the cause of failures. ### 3.3 Testing React Context * **Do This:** Create custom test providers to mock the context values and test components within a controlled context. Use "@testing-library/react" to render and interact with components. """typescript import { render, screen, fireEvent } from '@testing-library/react'; import { describe, expect, it } from 'vitest'; import React, { createContext, useContext, useState } from 'react'; // Context setup const CounterContext = createContext({ count: 0, setCount: (value: number) => {}, }); const useCounter = () => useContext(CounterContext); const CounterProvider = ({ children, initialCount = 0 }) => { const [count, setCount] = useState(initialCount); return ( <CounterContext.Provider value={{ count, setCount }}> {children} </CounterContext.Provider> ); }; // Component const CounterComponent = () => { const { count, setCount } = useCounter(); return ( <div> <span>{count}</span> <button onClick={() => setCount(count + 1)}>Increment</button> </div> ); }; describe('Counter Component with Context', () => { it('should display the initial count from context', () => { render( <CounterProvider initialCount={5}> <CounterComponent /> </CounterProvider> ); expect(screen.getByText('5')).toBeInTheDocument(); }); it('should increment the count when the button is clicked', () => { render( <CounterProvider initialCount={0}> <CounterComponent /> </CounterProvider> ); const incrementButton = screen.getByText('Increment'); fireEvent.click(incrementButton); expect(screen.getByText('1')).toBeInTheDocument(); }); it('should use a custom context value', () => { // Custom Provider for testing const TestProvider = ({ children }) => ( <CounterContext.Provider value={{ count: 100, setCount: () => {} }}> {children} </CounterContext.Provider> ); render( <TestProvider> <CounterComponent /> </TestProvider> ); expect(screen.getByText('100')).toBeInTheDocument(); }); }); """ * **Don't Do This:** Rely on the default context values during tests, as they might not accurately reflect the component's behavior in different scenarios. ## 4. Performance Considerations ### 4.1. Optimize State Setup * **Do This:** Minimize the amount of state that needs to be set up for each test. Only set up the state that is relevant to the specific test case. Use lazy initialization where possible. * **Don't Do This:** Create large, complex state objects unnecessarily. ### 4.2. Avoid Unnecessary State Updates * **Do This:** Only update the state when necessary. Avoid unnecessary state updates that can trigger re-renders or other performance-intensive operations. * **Don't Do This:** Continuously update state in a loop or in response to every event. ## 5. Security Considerations ### 5.1. Secure State Storage * **Do This:** If you are testing code that deals with sensitive data (e.g., passwords, API keys), ensure that the data is stored securely and is not exposed in test logs or reports. * **Don't Do This:** Store sensitive data in plain text or commit it to version control. Use environment variables or dedicated secrets management tools. ### 5.2. Input Validation * **Do This:** Test state updates with invalid or malicious input to ensure that the application handles errors gracefully and does not become vulnerable to security exploits. * **Don't Do This:** Assume that all input will be valid. ## 6. Code Style and Formatting * Follow established code style guidelines (e.g., Airbnb, Google) for whitespace, indentation, and naming conventions. * Use descriptive variable names to clearly indicate the purpose of the state being managed. * Add comments to explain complex state transitions or mocking strategies. ## 7. Conclusion By following these coding standards, developers can write more robust, maintainable, and performant tests for state management in Vitest. Adhering to these best practices will improve the overall quality of the codebase and reduce the risk of bugs and security vulnerabilities. Remember to always use the latest version of the stack and its libraries to maximize performance, security, and compatibility with the latest features. This document is intended as a living document, and it will be updated as new best practices and technologies emerge.

# Tooling and Ecosystem Standards for Vitest This document outlines coding standards specific to the Vitest testing framework, focusing on the tooling and ecosystem surrounding it. Adhering to these standards will enhance maintainability, readability, performance, and collaboration across projects utilizing Vitest. These standards are focused on the latest versions of Vitest and its related tooling. ## 1. IDE Integration and Configuration ### Standard: Use IDE integrations to enhance development workflow. * **Do This:** Configure your IDE with official Vitest extensions or plugins to provide real-time feedback, test execution, and debugging capabilities. * **Don't Do This:** Rely solely on command-line execution without leveraging IDE integrations for more efficient and interactive testing. **Why:** IDE integrations provide instant feedback, streamline debugging, and improve overall development efficiency. **Code Example (VS Code Configuration):** """json // .vscode/settings.json { "vitest.enable": true, "vitest.commandLine": "npx vitest", "vitest.include": ["**/*.{test,spec}.?(c|m)[jt]s?(x)"], "vitest.exclude": ["**/node_modules/**", "**/dist/**"] } """ **Explanation:** This configuration enables the Vitest extension in VS Code, sets the command-line execution path, and specifies the files to include and exclude from testing cycles. **Anti-Pattern:** Manually running tests via the command line for every small change. ### Standard: Configure file watching appropriately in your IDE. * **Do This:** Set up file watchers within your IDE to automatically trigger Vitest when relevant files change. * **Don't Do This:** Leave file watching disabled, forcing manual test runs after each code modification. **Why:** Automatic test execution drastically shortens the feedback loop during development. **Code Example (IDE-Specific Configuration - Generic description):** Consult your IDE's documentation on file watchers. Most IDEs have built-in or plugin-based systems that can detect file changes and run external tools, such as Vitest. For example, in WebStorm, use the "File Watchers" settings panel. """text // Example workflow: 1. Install the relevant Vitest plugin for your IDE. 2. Configure the plugin to watch specific file types (.js, .ts, .vue, etc.). 3. Set the Vitest command to run on file change (e.g., "npx vitest run"). """ **Anti-Pattern:** Waiting until the end of a coding session to run all tests. ## 2. Linters and Formatters ### Standard: Integrate linters and formatters with Vitest projects. * **Do This:** Use ESLint, Prettier, or similar tools to enforce consistent code style and catch potential errors. * **Don't Do This:** Neglect code style enforcement, resulting in inconsistent and potentially error-prone codebases. **Why:** Linters and formatters promote code consistency, reduce errors, and improve readability. **Code Example (ESLint Configuration):** """javascript // .eslintrc.js module.exports = { "env": { "browser": true, "es2021": true, "vitest/globals": true // Enables Vitest globals }, "extends": [ "eslint:recommended", "plugin:@typescript-eslint/recommended", "prettier" // Enables eslint-plugin-prettier and eslint-config-prettier. This will display prettier errors as ESLint errors. Make sure this is always the last configuration in the extends array. ], "parser": "@typescript-eslint/parser", "parserOptions": { "ecmaVersion": "latest", "sourceType": "module" }, "plugins": [ "@typescript-eslint", "vitest" ], "rules": { // Custom rules here } }; """ **Explanation:** This ESLint configuration includes TypeScript support, enables Vitest globals, and integrates Prettier for code formatting. The "vitest/globals" plugin automatically imports and configures Vitest's global APIs so that you don't have to import them manually within your test files. **Code Example (Prettier Configuration):** """javascript // .prettierrc.js module.exports = { semi: true, trailingComma: "all", singleQuote: true, printWidth: 120, tabWidth: 2, }; """ **Explanation:** This Prettier configuration sets basic formatting rules for semicolons, trailing commas, single quotes, line width, and tab width. **Anti-Pattern:** Ignoring linting errors and warnings, leading to potential bugs and code style inconsistencies. ### Standard: Implement pre-commit hooks to automatically run linters, formatters, and tests. * **Do This:** Use tools like Husky and lint-staged to ensure code quality before committing changes. * **Don't Do This:** Allow developers to commit code without automated checks, increasing the risk of introducing errors or style violations. **Why:** Pre-commit hooks enforce code quality, prevent broken builds, and automate repetitive tasks. **Code Example (Husky and lint-staged Configuration):** """json // package.json { "devDependencies": { "husky": "^8.0.0", "lint-staged": "^13.0.0" }, "scripts": { "prepare": "husky install", "test": "vitest" }, "lint-staged": { "*.{js,ts,vue}": [ "eslint --fix", "prettier --write", "git add" ], "*.{css,scss,md}": [ "prettier --write", "git add" ], "*.test.ts": [ "npm run test -- --relatedFiles $FILES" ] } } """ """bash # Enable husky npm install husky --save-dev npx husky install npm set-script prepare "husky install" npm run prepare # Add a pre-commit hook npx husky add .husky/pre-commit "npx lint-staged" """ **Explanation:** This configuration installs Husky and lint-staged, configures a pre-commit hook to run ESLint and Prettier on staged files, and runs the test suite against any changed test files. "prepare" script ensures husky is installed when the project is set up. This prevents commits with linting problems. **Anti-Pattern:** Skipping pre-commit hooks or disabling them entirely, negating their benefits. ## 3. Code Coverage ### Standard: Use code coverage tools to identify untested areas. * **Do This:** Integrate code coverage reporting into your Vitest workflow using tools like c8 or Istanbul. * **Don't Do This:** Disregard code coverage metrics, potentially leaving critical parts of the application untested. **Why:** Code coverage analysis helps identify gaps in testing and ensures comprehensive test suites. **Code Example (Vitest Configuration with Coverage):** """typescript // vitest.config.ts import { defineConfig } from 'vitest/config' export default defineConfig({ test: { environment: 'jsdom', coverage: { reporter: ['text', 'json', 'html'], all: true, // Ensure that all files are considered, even if not explicitly imported in a test file include: ['src/**'], // Files to consider for coverage exclude: ['src/**/*.d.ts'] // Files to exclude from coverage }, }, }) """ **Explanation:** This configuration enables code coverage reporting with multiple reporters (text, JSON, and HTML) and specifies the files to include and exclude. The "all: true" configuration is important to ensure full coverage reporting. **Anti-Pattern:** Aiming for 100% code coverage without considering the quality and relevance of the tests. Focus also on branch and path coverage. ### Standard: Set reasonable code coverage thresholds. * **Do This:** Define minimum code coverage thresholds (e.g., 80% for statements, branches, and functions) to maintain adequate test coverage. * **Don't Do This:** Ignore code coverage thresholds, allowing untested code to slip through, or setting unrealistically high targets that are difficult to achieve without sacrificing test quality. **Why:** Coverage thresholds enforce a minimum standard of test coverage and prevent regressions. **Code Example (Setting Coverage Thresholds):** While Vitest natively provides coverage reporting, enforcing thresholds often needs plugin integration. One common approach is integrating with tools during CI/CD. """bash # Example workflow (using a custom script or CI/CD pipeline): # 1. Run Vitest with coverage enabled. # 2. Parse the coverage report (e.g., using jq to extract coverage percentages from a JSON report). # 3. Fail the build if any coverage metric falls below the threshold. vitest run --coverage.enabled --coverage.reporter=json-summary # example using jq to validate in cicd: jq '.total.lines.pct > 80 and .total.statements.pct > 80' coverage-summary.json """ **Anti-Pattern:** Having no coverage thresholds, leading to low test coverage and increased risk of regressions. ## 4. Mocking and Stubbing Libraries ### Standard: Utilize mocking and stubbing libraries for isolating units of code. * **Do This:** Use "vi.mock()" in Vitest to mock dependencies and control their behavior during testing. * **Don't Do This:** Directly manipulate real dependencies or rely on global state, leading to brittle and unreliable tests. **Why:** Mocking allows for predictable and isolated testing, preventing external factors from influencing test results. **Code Example (Using "vi.mock()"):** """typescript // src/api.ts export async function fetchData() { const response = await fetch('https://example.com/data'); return response.json(); } // src/api.test.ts import { fetchData } from './api'; import { vi, describe, it, expect } from 'vitest'; describe('fetchData', () => { it('should return data from the API', async () => { const mockData = { message: 'Hello, world!' }; global.fetch = vi.fn().mockResolvedValue({ json: vi.fn().mockResolvedValue(mockData), }); const data = await fetchData(); expect(data).toEqual(mockData); expect(global.fetch).toHaveBeenCalledWith('https://example.com/data'); }); }); """ **Explanation:** This example mocks the "fetch" function and verifies that it is called with the correct URL and returns the expected data. **Anti-Pattern:** Over-mocking, which can lead to tests that are too tightly coupled to the implementation details and do not accurately reflect the system's behavior. ### Standard: Mock selectively and focus on external dependencies. * **Do This:** Mock external services, databases, or complex third-party libraries to simplify testing and avoid external dependencies. * **Don't Do This:** Mock internal implementation details or simple functions, which can make tests brittle and harder to maintain. **Why:** Mocking external dependencies isolates the unit under test and ensures that tests are not affected by external factors. **Code Example (Selective Mocking):** Instead of mocking the behavior of a function within the same module, focus on external dependencies. """typescript // src/service.ts import { fetchData } from './api'; export async function processData() { const data = await fetchData(); return data.message.toUpperCase(); } // src/service.test.ts import { processData } from './service'; import { fetchData } from './api'; import { vi, describe, it, expect } from 'vitest'; vi.mock('./api', () => { return { fetchData: vi.fn().mockResolvedValue({ message: 'mocked data' }), }; }); describe('processData', () => { it('should process data from the API', async () => { const result = await processData(); expect(result).toBe('MOCKED DATA'); expect(fetchData).toHaveBeenCalled(); }); }); """ **Explanation:** This example mocks the "fetchData" function from the "api" module, allowing the "processData" function to be tested in isolation. **Anti-Pattern:** Not using mocks when interacting with external services in unit tests, making the tests slow and dependent on external systems. ## 5. Test Runners and Configuration ### Standard: Configure Vitest to suit project requirements. * **Do This:** Customize Vitest's configuration options (e.g., "test.environment", "test.globals", "test.setupFiles") to optimize the testing environment. * **Don't Do This:** Use the default configuration without considering project-specific needs, potentially leading to suboptimal testing performance or compatibility issues. **Why:** Configuration options allow customization of the testing environment to suit specific project requirements. **Code Example (Vitest Configuration):** """typescript // vitest.config.ts import { defineConfig } from 'vitest/config' import { fileURLToPath } from 'node:url' import { resolve } from 'path' export default defineConfig({ resolve: { alias: { '@': fileURLToPath(new URL('./src', import.meta.url)) } }, test: { environment: 'jsdom', // or 'node' globals: true, setupFiles: ['./src/setupTests.ts'], include: ['**/*.{test,spec}.?(c|m)[jt]s?(x)'], exclude: ['node_modules', 'dist', '.idea', '.git', '.cache'], coverage: { reporter: ['html', 'text', 'json'], }, }, }) """ **Explanation:** This configuration sets the test environment to "jsdom", enables global variables, specifies setup files, and defines include/exclude patterns. It also configures coverage reporting. It adds an alias to make imports easier. **Anti-Pattern:** Setting the "environment" incorrectly (e.g. using "jsdom" in a Node.js backend project). ### Standard: Utilize Vitest's command-line interface (CLI) effectively. * **Do This:** Use CLI options (e.g., "--watch", "--run", "--filter", "--coverage") to control test execution and reporting. * **Don't Do This:** Rely solely on default test execution, missing opportunities to optimize testing workflows and target specific tests. **Why:** The CLI provides flexibility and control over test execution and reporting. **Code Example (Vitest CLI Usage):** """bash # Run all tests in watch mode npx vitest --watch # Run specific tests npx vitest ./src/components/MyComponent.test.ts # Run tests matching a pattern npx vitest --filter "MyComponent" # Generate coverage report npx vitest run --coverage """ **Explanation:** These commands demonstrate various CLI options for running tests in watch mode, targeting specific tests, filtering tests by name, and generating coverage reports. **Anti-Pattern:** Not using watch mode during development, which slows down the testing feedback loop. ## 6. CI/CD Integration ### Standard: Integrate Vitest into the CI/CD pipeline for automated testing. * **Do This:** Configure CI/CD pipelines (e.g., GitHub Actions, GitLab CI, Jenkins) to run Vitest tests on every commit or pull request. * **Don't Do This:** Manually run tests on local machines only, potentially missing regressions and delaying feedback. **Why:** CI/CD integration automates testing, prevents regressions, and ensures code quality throughout the development lifecycle. **Code Example (GitHub Actions Configuration):** """yaml # .github/workflows/test.yml name: Vitest Tests on: push: branches: [ main ] pull_request: branches: [ main ] jobs: test: runs-on: ubuntu-latest steps: - uses: actions/checkout@v3 - name: Setup Node.js uses: actions/setup-node@v3 with: node-version: 18 # Or your project's node version - name: Install dependencies run: npm install - name: Run tests run: npm run test -- --run # Ensure it runs all tests non-interactively - name: Upload coverage reports to Codecov uses: codecov/codecov-action@v3 with: token: ${{ secrets.CODECOV_TOKEN }} # Required for private repositories """ **Explanation:** This GitHub Actions workflow checks out the code, sets up Node.js, installs dependencies, runs Vitest tests, and uploads the coverage report to Codecov. **Anti-Pattern:** Not integrating tests into the CI/CD pipeline, which can lead to undetected regressions and lower code quality. ### Standard: Fail CI/CD builds on test failures. * **Do This:** Configure CI/CD pipelines to fail builds if any Vitest tests fail, preventing faulty code from being deployed. * **Don't Do This:** Allow CI/CD pipelines to pass despite test failures, creating the risk of deploying broken code to production. **Why:** Failing builds on test failures ensures that only working code is deployed to production. **Code Example (CI/CD Configuration - Generic example):** Most CI/CD platforms will automatically fail a build if the test command exits with a non-zero exit code. Vitest does this by default when tests fail. Ensure your CI/CD system is configured to detect non-zero exit codes and fail the build accordingly. No specific configuration is usually necessary, provided that "npm run test" (or equivalent) is the command that runs the tests. **Anti-Pattern:** Ignoring test failures in the CI/CD pipeline, potentially deploying broken code. ## 7. Reporting and Analytics ### Standard: Use reporting tools to visualize test results and track performance metrics. * **Do This:** Integrate Vitest with reporting tools like SonarQube, Codecov, or other code quality platforms to track test results, coverage metrics, and performance metrics over time. * **Don't Do This:** Rely solely on command-line output, missing opportunities to analyze trends and identify areas for improvement. **Why:** Reporting tools provide valuable insights into test performance, coverage trends, and code quality. **Code Example (Codecov Integration):** As shown in the GitHub Actions example above, Codecov can be easily integrated by uploading the coverage reports generated by Vitest. Ensure the "CODECOV_TOKEN" secret is properly configured. **Anti-Pattern:** Not tracking test performance and coverage metrics over time, making it difficult to identify and address regressions or performance bottlenecks. ### Standard: Set up notifications for test failures and performance regressions. * **Do This:** Configure CI/CD pipelines to send notifications (e.g., email, Slack) to developers when tests fail or performance regressions are detected. * **Don't Do This:** Rely on developers to manually check test results, potentially delaying the detection and resolution of issues. **Why:** Notifications ensure that developers are promptly informed of test failures and performance regressions, allowing them to address issues quickly. **Code Example (CI/CD Notifications - Generic example):** Most CI/CD platforms offer built-in notification mechanisms. Configure your platform to send email or Slack notifications to the relevant team members when a build fails. For example, in GitHub Actions: """yaml # .github/workflows/test.yml (continued) - name: Send Slack notification on failure if: failure() uses: rtCamp/action-slack-notify@v2 env: SLACK_CHANNEL: '#your-slack-channel' SLACK_WEBHOOK: ${{ secrets.SLACK_WEBHOOK }} """ **This example requires the "rtCamp/action-slack-notify" action and a properly configured "SLACK_WEBHOOK" secret.** Similar configurations exist for other CI/CD platforms. **Anti-Pattern:** Ignoring test failure notifications, leading to delayed issue resolution and potentially broken builds. By adhering to these tooling and ecosystem standards, development teams can maximize the benefits of Vitest, improve code quality, and streamline the testing process. Remember to keep up-to-date with the latest features and best practices in the Vitest ecosystem.

# API Integration Standards for Vitest This document outlines coding standards and best practices for integrating Vitest tests with backend services and external APIs, ensuring maintainable, performant, and secure testing. ## 1. General Principles ### 1.1 Use Mocking and Stubbing **Do This:** - Use mocking libraries like "vi.fn()" from Vitest or "sinon" to isolate unit tests from external dependencies. - Stub API calls to return predefined responses, preventing real API calls during testing. **Don't Do This:** - Directly call real APIs within unit tests. - Rely on external services being available or predictable during testing. **Why:** Mocking and stubbing ensure test isolation and repeatable results, which are crucial for unit testing. Avoid relying on the state of external services that could be unstable or change unexpectedly. **Example:** """typescript // src/apiClient.ts export async function fetchData(id: string): Promise<any> { const response = await fetch("https://api.example.com/data/${id}"); if (!response.ok) { throw new Error("HTTP error! status: ${response.status}"); } return await response.json(); } // src/apiClient.test.ts import { fetchData } from './apiClient'; import { describe, it, expect, vi } from 'vitest'; global.fetch = vi.fn(() => Promise.resolve({ ok: true, json: () => Promise.resolve({ id: '123', value: 'testData' }), }) ) as any; describe('fetchData', () => { it('fetches data correctly', async () => { const data = await fetchData('123'); expect(data).toEqual({ id: '123', value: 'testData' }); expect(fetch).toHaveBeenCalledWith('https://api.example.com/data/123'); }); it('handles errors correctly', async () => { (global.fetch as any).mockImplementationOnce(() => Promise.resolve({ ok: false, status: 404, }) ); await expect(fetchData('456')).rejects.toThrowError('HTTP error! status: 404'); }); }); """ ### 1.2 Separate Unit and Integration Tests **Do This:** - Classify tests based on scope: unit tests (isolated), integration tests (connecting components), and end-to-end tests (entire system). - Use different Vitest configurations or file naming conventions to distinguish between test types. **Don't Do This:** - Mix unit tests with integration tests in the same files. **Why:** Separation allows for faster feedback cycles for unit tests (mocked) and more comprehensive but slower tests for integration (potentially using real or test instances of APIs). **Example:** """ // vitest.config.unit.js export default { test: { include: ['src/**/*.unit.test.ts'], environment: 'node', }, }; // vitest.config.integration.js export default { test: { include: ['src/**/*.integration.test.ts'], environment: 'node', //setupFiles: ['./test/setupIntegration.ts'], // setup for integration tests (env vars etc.) timeout: 10000, // Longer timeout for integration tests }, }; """ File structure: """ src/ - apiClient.ts - apiClient.unit.test.ts // unit tests (mocked API calls) - apiClient.integration.test.ts // integration tests (potentially real API - use with caution) """ ### 1.3 Configuration Management **Do This:** - Use environment variables or configuration files to manage API endpoints and authentication keys. - Load environment variables using libraries like "dotenv" and make them available in your Vitest environment. **Don't Do This:** - Hardcode API endpoints or secrets directly in test code. - Commit sensitive information to version control. **Why:** Securely configuring test environments prevents exposing sensitive data and makes it easier to switch between test and production environments. **Example:** """typescript // .env.test API_ENDPOINT=https://test.example.com/api API_KEY=your_test_api_key """ """typescript // vitest.config.ts import { defineConfig } from 'vitest/config'; import 'dotenv/config'; // Load environment variables export default defineConfig({ test: { globals: true, environment: 'node', setupFiles: ['./test/setupEnv.ts'], }, }); // test/setupEnv.ts process.env.API_ENDPOINT = process.env.API_ENDPOINT || 'https://backup.example.com/api'; // src/apiClient.test.ts import { fetchData } from './apiClient'; import { describe, it, expect, vi } from 'vitest'; describe('fetchData', () => { it('uses the configured API endpoint', async () => { global.fetch = vi.fn().mockResolvedValue({ ok: true, json: () => Promise.resolve({ id: '123', value: 'testData' }), }); await fetchData('123'); expect(fetch).toHaveBeenCalledWith("${process.env.API_ENDPOINT}/data/123"); }); }); """ ## 2. Advanced Mocking Techniques ### 2.1 Mocking Modules **Do This:** - Use "vi.mock" to replace entire modules with mock implementations. - Create a separate mock module file with the same exports as the original. **Don't Do This:** - Mutate imported modules directly in test files without using "vi.mock". **Why:** "vi.mock" provides a cleaner and more maintainable way to mock modules, particularly if you aim to replace the entire module's functionality. **Example:** """typescript // src/apiClient.ts export async function externalFunction(id: string): Promise<string> { return "Actual result for ID: ${id}"; } // src/apiClient.test.ts import { externalFunction } from './apiClient'; import { describe, it, expect, vi } from 'vitest'; vi.mock('./apiClient', async () => { return { externalFunction: vi.fn().mockResolvedValue('Mocked Response'), }; }); describe('externalFunction', () => { it('should use the mocked function', async () => { const result = await externalFunction('123'); expect(result).toBe('Mocked Response'); }); }); """ ### 2.2 Mocking with Spies **Do This:** - Use "vi.spyOn" to monitor the behavior of specific functions or methods without replacing them entirely. - Verify that mocked functions are called with the correct arguments and number of times. **Don't Do This:** - Over-mock functions unless necessary; sometimes, observing behavior is sufficient. **Why:** Spies are useful when you want to verify how a function is used without completely altering its behavior. **Example:** """typescript // src/service.ts export class MyService { callExternalAPI(id: string): string { console.log("Calling API with id: ${id}"); return "API called for id: ${id}"; } } // src/service.test.ts import { MyService } from './service'; import { describe, it, expect, vi } from 'vitest'; describe('MyService', () => { it('should call the external API', () => { const service = new MyService(); const spy = vi.spyOn(service, 'callExternalAPI'); service.callExternalAPI('123'); expect(spy).toHaveBeenCalledWith('123'); expect(spy).toHaveBeenCalledTimes(1); }); }); """ ### 2.3 Asynchronous Mocking **Do This:** - Use "mockResolvedValue" or "mockRejectedValue" to mock asynchronous function responses. - Accurately simulate success and failure scenarios. **Don't Do This:** - Use synchronous mocking techniques for asynchronous functions. **Why:** Properly mocking asynchronous functions is crucial for testing asynchronous code paths in a non-blocking and deterministic way. **Example:** """typescript // src/apiClient.ts export async function fetchData(id: string): Promise<any> { await new Promise(resolve => setTimeout(resolve, 10)); // Simulate async operation const response = await fetch("https://api.example.com/data/${id}"); if (!response.ok) { throw new Error("HTTP error! status: ${response.status}"); } return await response.json(); } // src/apiClient.test.ts import { fetchData } from './apiClient'; import { describe, it, expect, vi } from 'vitest'; describe('fetchData', () => { it('mocks a resolved value', async () => { global.fetch = vi.fn().mockResolvedValue({ ok: true, json: () => Promise.resolve({ data: 'mocked' }), }); const result = await fetchData('123'); expect(result).toEqual({ data: 'mocked' }); }); it('mocks a rejected value', async () => { global.fetch = vi.fn().mockRejectedValue(new Error('API error')); await expect(fetchData('123')).rejects.toThrow('API error'); }); }); """ ## 3. Integration Testing Strategies ### 3.1 Test Databases **Do This:** - Use separate databases for testing and production environments. - Use tools like Docker or in-memory databases (like SQLite) to manage test databases. - Seed the test database with known data before running tests. - Clean up the test database after each test run. **Don't Do This:** - Run tests against the production database. - Leave test data in the database after tests are complete. **Why:** Ensures tests do not affect production data and that tests are repeatable. **Example:** """typescript // test/setupIntegration.ts import { beforeAll, afterAll } from 'vitest'; import { Sequelize } from 'sequelize'; const sequelize = new Sequelize('test_db', 'user', 'password', { dialect: 'sqlite', storage: ':memory:', // Use an in-memory database logging: false, }); beforeAll(async () => { await sequelize.sync({ force: true }); // Create tables and drop existing // Seed the database (example): // await MyModel.bulkCreate([{ name: 'Test Data' }]); }); afterAll(async () => { await sequelize.close(); }); export { sequelize }; """ ### 3.2 API Contracts **Do This:** - Document API contracts using tools like OpenAPI/Swagger. - Validate API responses in integration tests against the documented contract. **Don't Do This:** - Assume API responses will always match expectations without verification. **Why:** Ensures API changes are caught during testing and prevents integration issues. **Example:** """typescript // src/apiClient.integration.test.ts import { fetchData } from './apiClient'; import { describe, it, expect } from 'vitest'; import {validate} from 'jsonschema'; const apiResponseSchema = { type: 'object', properties: { id: { type: 'string' }, value: { type: 'string' }, }, required: ['id', 'value'], }; describe('fetchData Integration', () => { it('fetches data and validates the API response', async () => { const data = await fetchData('123'); const validationResult = validate(data, apiResponseSchema); expect(validationResult.valid).toBe(true); expect(data).toHaveProperty('id'); expect(data).toHaveProperty('value'); }); }); """ ### 3.3 Test Doubles **Do This:** - Use test doubles like mocks, stubs, and spies strategically to control external dependencies during integration tests. - Use fakes and dummies when simple replacements are needed and behavior verification is not. **Don't Do This:** - Overuse test doubles, which can make tests too complex. **Why:** Effectively manages dependencies, making tests both more reliable and deterministic. ## 4. Security Considerations ### 4.1 Data Sanitization **Do This:** - Sanitize test data to prevent security vulnerabilities like SQL injection or XSS. - Avoid using real user data in tests. **Don't Do This:** - Directly use unsanitized data from external sources in tests. **Why:** Prevents accidental introduction or masking of security vulnerabilities. **Example:** """typescript import { sanitize } from 'dompurify'; describe('Data Sanitization', () => { it('should sanitize potentially malicious input', () => { const maliciousInput = '<img src="x" onerror="alert(\'XSS\')">'; const sanitizedInput = sanitize(maliciousInput); expect(sanitizedInput).toBe('<img src="x">'); // Sanitized output }); }); """ ### 4.2 Authentication and Authorization **Do This:** - Mock authentication and authorization mechanisms to avoid using real credentials in tests. - Verify that authorized users can access specific endpoints. - Create separate test accounts with limited privileges. **Don't Do This:** - Use production credentials in test environments. - Skip authorization checks in tests. **Why:** Proper testing ensures authentication and authorization mechanisms work as expected without compromising security. ## 5. Performance Testing with Vitest ### 5.1 Measuring Execution Time **Do This:** - Use "performance.now()" or "performance.mark()" to measure the execution time of API calls during integration tests. - Set performance thresholds and fail tests if execution time exceeds the threshold. **Don't Do This:** - Neglect performance testing and solely focus on functionality. **Why:** Identifies performance bottlenecks and ensures API calls meet performance requirements. **Example:** """typescript import { describe, it, expect } from 'vitest'; import { fetchData } from './apiClient'; describe('Performance Testing', () => { it('should execute within a specified time limit', async () => { const startTime = performance.now(); await fetchData('123'); const endTime = performance.now(); const executionTime = endTime - startTime; const performanceThreshold = 200; // Milliseconds expect(executionTime).toBeLessThan(performanceThreshold); }); }); """ ### 5.2 Load Testing Simulation **Do This:** - Simulate concurrent API calls to assess performance under load. - Use libraries like "p-map" to control concurrency. **Don't Do This:** - Neglect load testing, which can reveal scalability issues. **Why:** Uncovers performance issues that only manifest under load. ## 6. Best Practices for Maintainability ### 6.1 Descriptive Test Names **Do This:** - Use clear and concise test names that describe the expected behavior. - Include relevant information, such as input values and expected output. **Don't Do This:** - Use generic or vague test names that do not provide context. **Why:** Improves readability and makes it easier to understand test failures. **Example:** """typescript it('should fetch data successfully with a valid ID', async () => { // ... }); it('should throw an error when fetching data with an invalid ID', async () => { // ... }); """ ### 6.2 Test Data Management **Do This:** - Use factories or fixtures to generate test data consistently. - Keep test data separate from test logic. **Don't Do This:** - Hardcode test data directly in test cases. **Why:** Simplifies test maintenance and prevents duplication of test data. ### 6.3 Clean Test Code **Do This:** - Follow the DRY (Don't Repeat Yourself) principle in test code. - Refactor common setup logic into helper functions or reusable modules. - Keep test cases focused and concise. **Don't Do This:** - Write redundant or overly complex test code. **Why:** Simplifies test code and reduces the likelihood of errors. By following these standards, you'll create a robust, maintainable, and secure Vitest testing environment for your API integrations.

# Testing Methodologies Standards for Vitest This document outlines the coding standards for testing methodologies using Vitest. These standards aim to ensure consistent, maintainable, performant, and secure tests across our projects. This document covers strategies for unit, integration, and end-to-end tests with Vitest. ## 1. Testing Pyramid & Levels of Testing ### 1.1. Standard: Adhere to the Testing Pyramid * **Do This:** Prioritize unit tests. Strive for a higher number of unit tests compared to integration or end-to-end tests. Reduce the number of end-to-end tests. * **Don't Do This:** Create a "top-heavy" testing pyramid with a large number of slow, brittle end-to-end tests. * **Why:** Unit tests are faster and more granular, leading to quicker feedback and easier debugging. End-to-end tests are slower, less specific, and more likely to break due to UI changes or environment issues. ### 1.2. Unit Tests * **Standard:** Unit tests should focus on testing a single unit of code in isolation (e.g., a function, a class method). * **Do This:** Mock dependencies to isolate the unit under test. * **Don't Do This:** Perform database operations, network requests, or file system accesses directly in unit tests. * **Why:** Isolating units makes tests faster and more reliable. Dependencies can introduce external factors that make tests flaky or slow. """typescript // Example: Unit test for a function that formats a date import { formatDate } from '../src/utils'; import { describe, expect, it, vi } from 'vitest'; describe('formatDate', () => { it('should format a date correctly', () => { const mockDate = new Date('2024-01-01T12:00:00.000Z'); vi.spyOn(global, 'Date').mockImplementation(() => mockDate); // mock Date object, to ensure date is always the same for testing expect(formatDate(new Date())).toBe('2024-01-01'); // now it won't be "new Date()", but mockDate. }); it('should handle different date objects', () => { const date = new Date('2024-02-15T08:30:00.000Z'); expect(formatDate(date)).toBe('2024-02-15'); }); }); """ ### 1.3. Integration Tests * **Standard:** Integration tests should verify the interaction between different components or modules. * **Do This:** Make API calls within your application and mock the external service responses. * **Don't Do This:** Test intricate business logic which should go into unit tests if possible. * **Why:** Validates that modules work together as expected, ensuring the larger system functions correctly. """typescript // Example: Integration test for an API client import { describe, expect, it, vi } from 'vitest'; import { fetchUserData } from '../src/apiClient'; global.fetch = vi.fn(() => Promise.resolve({ json: () => Promise.resolve({ id: 1, name: 'John Doe' }), }) ) as any; describe('fetchUserData', () => { it('should fetch user data from the API', async () => { const userData = await fetchUserData(1); expect(userData).toEqual({ id: 1, name: 'John Doe' }); expect(fetch).toHaveBeenCalledWith('/api/users/1'); }); it('should handle API errors', async () => { (fetch as any).mockImplementationOnce(() => Promise.reject('API Error')); await expect(fetchUserData(1)).rejects.toEqual('API Error'); }); }); """ ### 1.4. End-to-End (E2E) Tests * **Standard:** E2E tests should simulate real user interactions to validate the entire application flow. * **Do This:** Use tools like Playwright or Cypress for browser automation. Test critical user journeys. * **Don't Do This:** Use slow, brittle E2E tests for verifying logic that can be easily unit-tested. * **Why:** E2E tests provide confidence that the entire system works correctly from the user's perspective. """typescript // Example: Playwright E2E Test import { test, expect } from '@playwright/test'; test('Homepage has title', async ({ page }) => { await page.goto('http://localhost:3000/'); await expect(page).toHaveTitle("My App"); }); test('Navigation to about page', async ({ page }) => { await page.goto('http://localhost:3000/'); await page.getByRole('link', { name: 'About' }).click(); await expect(page).toHaveURL(/.*about/); }); """ ## 2. Test Structure and Organization ### 2.1. Standard: Arrange, Act, Assert (AAA) Pattern * **Do This:** Structure your tests into three distinct parts: Arrange (setup the test environment), Act (execute the code being tested), and Assert (verify the expected outcome). * **Don't Do This:** Mix setup, execution, and verification logic within a single block of code. * **Why:** AAA makes tests more readable, maintainable, and easier to understand. """typescript // Example: AAA pattern import { describe, expect, it } from 'vitest'; import { add } from '../src/math'; describe('add', () => { it('should add two numbers correctly', () => { // Arrange const a = 5; const b = 3; // Act const result = add(a, b); // Assert expect(result).toBe(8); }); }); """ ### 2.2. Standard: Test File Structure * **Do This:** Create a "test" directory mirroring your "src" directory for test files. Use "*.test.ts" or "*.spec.ts" naming convention. * **Don't Do This:** Place test files directly alongside source files. * **Why:** A consistent file structure makes it easier to locate and maintain tests. """ src/ components/ Button.tsx utils/ formatDate.ts test/ components/ Button.test.tsx utils/ formatDate.test.ts """ ### 2.3. Standard: Descriptive Test Names * **Do This:** Write descriptive test names that clearly explain what the test is verifying. Follow a convention like "should [verb] [expected result] when [scenario]". * **Don't Do This:** Use generic, unclear, or vague test names. * **Why:** Clear test names facilitate debugging and give a good overview of the tested functionality. """typescript // Good: it('should return "Hello, World!" when no name is provided', () => { /* ... */ }); // Bad: it('test', () => { /* ... */ }); """ ### 2.4. Standard: Grouping Tests with 'describe' * **Do This:** Use the "describe" block to group related tests for clarity and organization. * **Don't Do This:** Create a single, monolithic test file with no logical grouping. * **Why:** "describe" blocks improve test readability and help identify the area of the code being tested. """typescript import { describe, expect, it } from 'vitest'; import { calculateDiscount } from '../src/utils'; describe('calculateDiscount', () => { it('should apply a 10% discount for orders over $100', () => { expect(calculateDiscount(150)).toBe(15); }); it('should not apply a discount for orders under $100', () => { expect(calculateDiscount(50)).toBe(0); }); }); """ ## 3. Mocking and Stubbing ### 3.1. Standard: Minimize Mocking * **Do This:** Use mocks only when necessary to isolate the unit under test. Prefer real dependencies when possible. * **Don't Do This:** Mock everything by default. Over-mocking can blur the line between implementation change and test update. * **Why:** Reduces the risk of false positives and increases confidence in the tests' accuracy. ### 3.2. Standard: Use Vitest's Built-in Mocking * **Do This:** Use "vi.mock", "vi.spyOn", and "vi.fn" for mocking and stubbing in Vitest. * **Don't Do This:** Use external mocking libraries that may not be compatible with Vitest. * **Why:** Vitest's built-in mocking is well-integrated and performant. """typescript // Example: Mocking a module function import { describe, expect, it, vi } from 'vitest'; import { fetchData } from '../src/dataService'; import { processData } from '../src/processor'; vi.mock('../src/dataService', () => ({ fetchData: vi.fn(() => Promise.resolve([{ id: 1, name: 'Test Data' }])), })); describe('processData', () => { it('should process data from the dataService', async () => { const result = await processData(); expect(result).toEqual([{ id: 1, name: 'Processed Test Data' }]); }); }); """ ### 3.3. Standard: Restore Mocks After Each Test * **Do This:** Use "vi.restoreAllMocks()" (or "afterEach(vi.restoreAllMocks())") to reset mocks after each test. * **Don't Do This:** Leave mocks active between tests, which can lead to unexpected behavior and test pollution. * **Why:** Prevents interference between tests and ensures reliable results. """typescript import { describe, expect, it, vi, afterEach } from 'vitest'; import { externalService } from '../src/externalService'; import { myModule } from '../src/myModule'; describe('myModule', () => { afterEach(() => { vi.restoreAllMocks(); }); it('should call externalService correctly', () => { const spy = vi.spyOn(externalService, 'doSomething'); myModule.run(); expect(spy).toHaveBeenCalled(); }); it('should handle errors from externalService', async () => { vi.spyOn(externalService, 'doSomething').mockRejectedValue(new Error('Service Unavailable')); await expect(myModule.run()).rejects.toThrowError('Service Unavailable'); }); }); """ ### 3.4 Standard: Mocking In-Source Testing * **Do This:** Use "import.meta.vitest" inside of the scope you want to test. Run tests directly within component or module. * **Why:** Tests share the same scope making them able to test against private states. """typescript // src/index.ts export const add = (a: number, b: number) => a + b if (import.meta.vitest) { const { it, expect } = import.meta.vitest it('add', () => { expect(add(1, 2)).eq(3) }) } """ ## 4. Asynchronous Testing ### 4.1. Standard: Use "async/await" for Asynchronous Operations * **Do This:** Use "async" and "await" to handle asynchronous operations in your tests. * **Don't Do This:** Rely on callbacks or Promises without "async/await", which can make tests harder to read and debug. * **Why:** "async/await" makes asynchronous code look and behave more like synchronous code, improving readability and maintainability. """typescript // Example: Testing an asynchronous function import { describe, expect, it } from 'vitest'; import { fetchData } from '../src/apiClient'; describe('fetchData', () => { it('should fetch data successfully', async () => { const data = await fetchData('https://example.com/api/data'); expect(data).toBeDefined(); }); it('should handle errors when fetching data', async () => { try { await fetchData('https://example.com/api/error'); } catch (error: any) { expect(error.message).toBe('Failed to fetch data'); } }); }); """ ### 4.2. Standard: Handle Promises with "expect.resolves" and "expect.rejects" * **Do This:** Use "expect.resolves" to assert that a Promise resolves with a specific value, and "expect.rejects" to assert that a Promise rejects with a specific error. * **Don't Do This:** Use "try/catch" for successful asynchronous calls. * **Why:** "expect.resolves" and "expect.rejects" provide a more concise and readable way to test Promises. """typescript import { describe, expect, it } from 'vitest'; import { createUser } from '../src/userService'; describe('createUser', () => { it('should create a user successfully', async () => { await expect(createUser('john.doe@example.com')).resolves.toBe('user123'); }); it('should reject with an error if the email is invalid', async () => { await expect(createUser('invalid-email')).rejects.toThrowError('Invalid email format'); }); }); """ ### 4.3. Standard: Use Fake Timers for Time-Dependent Tests * **Do This:** Use "vi.useFakeTimers()" with "vi.advanceTimersByTime()" to control the passage of time in your tests. * **Don't Do This:** Rely on "setTimeout" or "setInterval" with real timers, which can make tests slow and unreliable. * **Why:** Fake timers make time-dependent tests faster, more deterministic, and easier to control. """typescript import { describe, expect, it, vi, beforeEach } from 'vitest'; import { delayedFunction } from '../src/utils'; describe('delayedFunction', () => { beforeEach(() => { vi.useFakeTimers(); }); it('should execute the callback after a delay', () => { let executed = false; delayedFunction(() => { executed = true; }, 1000); expect(executed).toBe(false); vi.advanceTimersByTime(1000); expect(executed).toBe(true); }); it('should execute the callback at least after a delay of x milliseconds', () => { const callback = vi.fn(); delayedFunction(callback, 1000); vi.advanceTimersByTime(999); expect(callback).not.toHaveBeenCalled(); // not called yet vi.advanceTimersByTime(1); // advance another 1 ms expect(callback).toHaveBeenCalled(); // now is called }) }); """ ## 5. Test Data Management ### 5.1. Standard: Use Test Data Factories or Fixtures * **Do This:** Create test data factories or fixtures to generate consistent and reusable test data. * **Don't Do This:** Hardcode test data directly in your tests, leading to duplication and maintenance issues. * **Why:** Test data factories make it easier to create complex test data structures and ensure consistency across tests. """typescript // Example: Test data factory import { faker } from '@faker-js/faker'; export const createUser = (overrides = {}) => ({ id: faker.number.int(), email: faker.internet.email(), name: faker.person.fullName(), ...overrides, }); //Use it in your tests: import { describe, expect, it } from 'vitest'; import { createUser } from './factories'; describe('User', () => { it('should create a valid user', () => { const user = createUser(); expect(user).toHaveProperty('id'); expect(user).toHaveProperty('email'); }); it('should allow overriding properties', () => { const user = createUser({ name: 'Custom Name' }); expect(user.name).toBe('Custom Name'); }); }); """ ### 5.2. Standard: Avoid Sharing Test Data * **Do This:** Create new test data for each test case to avoid interference between tests. If you must, use a method like the "beforeEach" hook. * **Don't Do This:** Mutate shared test data, which can lead to unpredictable test results and flaky tests. * **Why:** Prevents test pollution and ensures that each test case is independent and reliable. ### 5.3. Standard: Seed Your Testing Database Before Tests * **Do This:** Seed database with a known state before any tests are run. * **Don't Do This:** Allow tests to create dependencies on each other's data and state. * **Why:** Ensures tests have a consistent, predictable, isolated environment. """typescript // Example: Seeding database before running tests import { describe, expect, it, beforeAll, afterAll } from 'vitest'; import { seedDatabase, clearDatabase } from './db'; // your database setup file import { User } from '../src/models/User'; describe('User Model', () => { beforeAll(async () => { await seedDatabase(); // Seed the database with consistent test data }); afterAll(async () => { await clearDatabase(); // Clear the database after all tests are complete }); it('should create a user correctly', async () => { const newUser = await User.create({ name: 'Test User', email: 'test@example.com' }); expect(newUser.name).toBe('Test User'); }); it('should find a user by email', async () => { const user = await User.findOne({ where: { email: 'test@example.com' } }); expect(user).toBeDefined(); }); }); """ ## 6. Performance Testing ### 6.1. Standard: Use "performance.mark" and "performance.measure" for Performance Measurement * **Do This:** Utilize the "performance.mark" and "performance.measure" APIs to measure the execution time of critical code sections. * **Don't Do This:** Rely on manual time tracking or inaccurate timing methods. * **Why:** Provides precise performance metrics for optimizing code execution. """typescript import { describe, expect, it } from 'vitest'; import { expensiveFunction } from '../src/utils'; describe('expensiveFunction', () => { it('should execute within a reasonable time', () => { performance.mark('start'); expensiveFunction(); performance.mark('end'); const measure = performance.measure('expensiveFunction', 'start', 'end'); expect(measure.duration).toBeLessThan(100); // Milliseconds }); }); """ ### 6.2. Standard: Threshold-Based Assertions * **Do This:** Set thresholds or performance budgets by setting "expect(measure.duration).toBeLessThan(100)". * **Don't Do This:** Test performance in an unmeasurable relative "it's fast" way. * **Why:** Prevents performance regressions by ensuring code executes within acceptable time limits. ## 7. Security Considerations ### 7.1. Standard: Avoid Hardcoding Secrets in Tests * **Do This:** Use environment variables or configuration files to store sensitive information used in tests. * **Don't Do This:** Hardcode API keys, passwords, or other secrets directly in your test code. * **Why:** Protects sensitive information from exposure and reduces the risk of security breaches. ### 7.2. Standard: Sanitize Test Inputs * **Do This:** Sanitize test inputs to prevent injection attacks or other security vulnerabilities. * **Don't Do This:** Use unsanitized user inputs directly in your tests, which can introduce security risks. * **Why:** Helps identify potential security vulnerabilities in your code and prevent real-world attacks. Added security can come from "vi.fn()" mocking return or argument sanitization. ### 7.3 Standard: Mock Authentication and Authorization * **Do This:** Mock authentication and authorization services during tests to avoid making real external calls. * **Why:** Prevents sensitive credentials from use and allows for specific permissions to be tested. """typescript // Example: Mock Authenticated User import { describe, expect, it, vi } from 'vitest'; import { getUserProfile } from '../src/authService'; import { getRestrictedData } from '../src/dataService'; vi.mock('../src/authService', () => ({ getUserProfile: vi.fn(() => ({ id: 'mocked-user', isAdmin: true })) }); describe('accessControlTesting', () => { it('should allow access for admin users', async () => { const profile = await getUserProfile(); const data = await getRestrictedData(profile.id); expect(data).toBeDefined(); }); }); """ ## 8. Continuous Integration (CI) ### 8.1. Standard: Run Tests on Every Commit * **Do This:** Configure your CI/CD pipeline to automatically run all tests on every commit or pull request. * **Don't Do This:** Only run tests manually or on a schedule, which can delay feedback and increase the risk of regressions. * **Why:** Provides immediate feedback on code changes and prevents regressions from making their way into production. ### 8.2. Standard: Use a Dedicated Test Environment * **Do This:** Run tests in a dedicated environment that is isolated from other processes and has a known configuration. * **Don't Do This:** Run tests in a shared environment or on your local machine, which can introduce inconsistencies and dependencies. * **Why:** Ensures consistent and reliable test results, regardless of the environment. ### 8.3 Standard: Utilize Vitest CLI Flags in CI * **Do This:** Use "--run" and "--reporter=junit" to ensure tests are running correctly on the CI process. JUnit provides a way to look back at test results. ## 9. Code Coverage ### 9.1. Standard: Aim for High Code Coverage * **Do This:** Strive for high code coverage (e.g., 80% or higher) to ensure that most of your code is being tested. * **Don't Do This:** Focus solely on code coverage metrics without considering the quality and effectiveness of your tests. * **Why:** Provides a measure of how much of your code is being tested and helps identify areas that may need more coverage. ### 9.2. Standard: Use "--coverage" Flag for Coverage Reports * **Do This:** Use the "--coverage" flag in Vitest to generate code coverage reports. * **Don't Do This:** Rely on external coverage tools that may not be compatible with Vitest. * **Why:** Provides detailed information about code coverage, including line, branch, and function coverage. ## 10. Test Doubles Test doubles mimic real components for testing purposes. Common types include: * **Stubs:** Provide predefined responses to calls. * **Mocks:** Verify interactions and behaviors. * **Spies:** Track how a function or method is used. * **Fakes:** Simplified implementations of a component. * **Dummies:** Pass placeholders when a value is needed but not used. ### 10.1 Standard: Use Doubles to Verify Proper Code Execution * **Do This:** Mock components or functions and verify those mocks got called as expected. * **Why:** Allows for test driven development when mocking. Helps isolate code. """typescript // mock axios and check if it gets called with the correct URL" import axios from 'axios'; import { fetchData } from '../src/apiFunctions'; vi.mock('axios'); it('fetches data from the correct URL', async () => { const mockAxios = vi.mocked(axios); mockAxios.get.mockResolvedValue({ data: { message: 'Success!' } }); const result = await fetchData('test-url'); expect(mockAxios.get).toHaveBeenCalledWith('test-url'); expect(result).toEqual({ message: 'Success!' }); }); """

# Component Design Standards for Vitest This document outlines the coding standards for component design within the Vitest testing framework. It aims to guide developers in creating reusable, maintainable, and performant test components. These standards are tailored to the latest features and best practices of Vitest. ## 1. Componentization Principles in Vitest This section establishes the fundamental principles underlying effective component design within the context of Vitest. ### 1.1. Abstraction and Encapsulation * **Standard:** Encapsulate complex testing logic within reusable components. Abstract away implementation details to simplify test setup and assertions. * **Why:** Reduces duplication, improves readability, and makes tests more resilient to changes in the underlying system. * **Do This:** Create helper functions or custom matchers to handle common assertion patterns. * **Don't Do This:** Repeat the same setup or assertion logic across multiple test files. """typescript // Good: Abstraction with a custom matcher import { expect } from 'vitest'; expect.extend({ toBeWithinRange(received, floor, ceiling) { const pass = received >= floor && received <= ceiling; if (pass) { return { message: () => "expected ${received} not to be within range ${floor} - ${ceiling}", pass: true, }; } else { return { message: () => "expected ${received} to be within range ${floor} - ${ceiling}", pass: false, }; } }, }); // Use the custom matcher it('number should be within range', () => { expect(100).toBeWithinRange(90, 110); }); // Bad: Repeating assertion logic it('number should be within range (bad)', () => { const number = 100; const floor = 90; const ceiling = 110; expect(number >= floor && number <= ceiling).toBe(true); }); """ ### 1.2. Single Responsibility Principle (SRP) * **Standard:** Each test component or helper should have one, and only one, reason to change. * **Why:** Promotes modularity, reduces complexity, and makes it easier to isolate and fix issues. * **Do This:** Break down large, monolithic test functions into smaller, more focused components. * **Don't Do This:** Create test functions that handle multiple aspects of a component's behavior. """typescript // Good: SRP - Separate setup and assertion logic import { describe, it, expect, beforeEach } from 'vitest'; describe('MyComponent', () => { let component; beforeEach(() => { component = { /* ... */ }; // Simulate component initialization }); it('should render correctly', () => { expect(component).toBeDefined(); // Assertion logic }); it('should handle user input', () => { // Test input handling expect(true).toBe(true); }); }); // Bad: Violating SRP - Mixing setup and assertions it('MyComponent - should render and handle input (BAD)', () => { const component = { /* ... */ }; // Setup expect(component).toBeDefined(); // Assertion // Test input handling expect(true).toBe(true); }); """ ### 1.3. Composition over Inheritance * **Standard:** Prefer composing test components from smaller, reusable parts rather than relying on deep inheritance hierarchies. * **Why:** Improves flexibility, reduces coupling, and avoids the complexities of inheritance. * **Do This:** Create utility functions that encapsulate specific testing behaviors and compose them as needed. * **Don't Do This:** Create deeply nested inheritance structures for your test components. """typescript // Good: Composition using utility functions import { describe, it, expect } from 'vitest'; const createMockComponent = (props = {}) => ({ ...props, isMock: true }); const assertComponentRenders = (component) => expect(component).toBeDefined(); describe('ComposableComponent', () => { it('should create a mock component', () => { const mock = createMockComponent({ name: 'Test' }); expect(mock.name).toBe('Test'); expect(mock.isMock).toBe(true); }); it('should assert if the component renders', () => { const mockComponent = createMockComponent(); assertComponentRenders(mockComponent); }); }); """ ## 2. Creating Reusable Components in Vitest This section focuses on the specific techniques and best practices for creating modular, easily reusable components for your tests. ### 2.1. Custom Matchers * **Standard:** Utilize custom matchers to encapsulate complex or domain-specific assertions. * **Why:** Improves test readability, reduces code duplication, and provides a more expressive API for your tests. * **Do This:** Implement custom matchers for common validation scenarios like date formatting or data structure validation. * **Don't Do This:** Hardcode complex assertion logic directly within your tests. """typescript // Custom Matcher Example import { expect } from 'vitest'; expect.extend({ toBeValidDate(received) { const pass = received instanceof Date && !isNaN(received.getTime()); if (pass) { return { message: () => "expected ${received} not to be a valid date", pass: true, }; } else { return { message: () => "expected ${received} to be a valid date", pass: false, }; } }, }); it('should be a valid date', () => { expect(new Date()).toBeValidDate(); }); """ ### 2.2. Test Factories * **Standard:** Use test factories to create consistent and configurable test data. * **Why:** Reduces boilerplate code, makes tests more maintainable, and allows for easy customization of test scenarios. * **Do This:** Create factory functions for generating mock data or component props. * **Don't Do This:** Hardcode test data directly within your tests. """typescript // Test Factory Example import { describe, it, expect } from 'vitest'; const createMockUser = (overrides = {}) => ({ id: '123', name: 'Test User', email: 'test@example.com', ...overrides, }); describe('User Creation', () => { it('should create a default user', () => { const user = createMockUser(); expect(user.id).toBe('123'); expect(user.name).toBe('Test User'); }); it('should allow overrides', () => { const user = createMockUser({ name: 'Custom Name' }); expect(user.name).toBe('Custom Name'); }); }); """ ### 2.3. Test Data Builders * **Standard:** Employ test data builders for constructing complex, nested test data objects in a readable and maintainable way. * **Why:** Simplifies the creation of intricate test data structures, promoting clarity and reducing the likelihood of errors. * **Do This:** Implement builder classes or functions to manage the construction of complex test data scenarios. * **Don't Do This:** Manually construct complex test data objects within test cases, leading to verbose and error-prone tests. """typescript // Test Data Builder Example import { describe, it, expect } from 'vitest'; class UserBuilder { private id: string = '123'; private name: string = 'Test User'; private email: string = 'test@example.com'; private addresses: string[] = []; withId(id: string): UserBuilder { this.id = id; return this; } withName(name: string): UserBuilder { this.name = name; return this; } withEmail(email: string): UserBuilder { this.email = email; return this; } withAddress(address: string): UserBuilder { this.addresses.push(address); return this; } build(): any { return { id: this.id, name: this.name, email: this.email, addresses: this.addresses, }; } } describe('UserBuilder', () => { it('should build a user with default values', () => { const user = new UserBuilder().build(); expect(user.id).toBe('123'); expect(user.name).toBe('Test User'); expect(user.email).toBe('test@example.com'); expect(user.addresses).toEqual([]); }); it('should build a user with custom values', () => { const user = new UserBuilder() .withId('456') .withName('Jane Doe') .withEmail('jane.doe@example.com') .withAddress('123 Main St') .build(); expect(user.id).toBe('456'); expect(user.name).toBe('Jane Doe'); expect(user.email).toBe('jane.doe@example.com'); expect(user.addresses).toEqual(['123 Main St']); }); }); """ ### 2.4. Page Objects (for UI Testing) * **Standard:** Create page object classes to represent UI elements and interactions. Use with libraries like Playwright or Cypress when testing UI components. * **Why:** Isolates UI-specific logic, making tests more resilient to UI changes and improving maintainability. * **Do This:** Define page object classes that encapsulate locators, actions, and assertions for specific UI pages or components. * **Don't Do This:** Directly interact with UI elements within your tests. """typescript // Hypothetical Page Object Example (with Playwright) import { expect, Page } from '@playwright/test'; class LoginPage { private readonly page: Page; private readonly usernameInput = '#username'; private readonly passwordInput = '#password'; private readonly loginButton = '#login-button'; constructor(page: Page) { this.page = page; } async goto() { await this.page.goto('/login'); } async login(username, password) { await this.page.fill(this.usernameInput, username); await this.page.fill(this.passwordInput, password); await this.page.click(this.loginButton); } async assertLoginSuccess() { await expect(this.page.locator('#success-message')).toBeVisible(); } } export { LoginPage }; // In your test: import { test } from '@playwright/test'; import { LoginPage } from './LoginPage'; test('Login should succeed', async ({ page }) => { const loginPage = new LoginPage(page); await loginPage.goto(); await loginPage.login('testuser', 'password'); await loginPage.assertLoginSuccess(); }); """ ## 3. Maintaining Test Components This section deals with strategies for keeping test components up-to-date, easy-to-understand, and performant, along with addressing common anti-patterns. ### 3.1. Test Component Documentation * **Standard:** Document your test helper functions, custom matchers, and test factories using JSDoc or TypeScriptDoc. * **Why:** Improves the understandability of your test code and makes it easier for other developers (and your future self) to use and maintain. * **Do This:** Add comments explaining the purpose, usage, and parameters of your test components. * **Don't Do This:** Leave your test components undocumented. """typescript /** * Creates a mock user object. * * @param {object} overrides - Optional properties to override the default values. * @returns {object} A mock user object. */ const createMockUser = (overrides = {}) => ({ id: '123', name: 'Test User', email: 'test@example.com', ...overrides, }); """ ### 3.2. Consistent Naming Conventions * **Standard:** Use consistent and descriptive names for your test components. * **Why:** Makes your test code easier to read and understand. * **Do This:** Use prefixes like "mock", "stub", or "fake" to indicate the purpose of your test components. * **Don't Do This:** Use ambiguous or inconsistent names. """typescript // Good: Consistent Naming const mockApiService = () => ({ getData: vi.fn().mockResolvedValue([{ id: 1, name: 'Item 1' }]), }); describe('MyComponent', () => { it('should fetch data correctly', async () => { const api = mockApiService(); //Use of appropriate naming //..rest of test }); }); //Bad: Inconsistent Naming const apiService = () => ({ getData: vi.fn().mockResolvedValue([{ id: 1, name: 'Item 1' }]), }); describe('MyComponent', () => { it('should fetch data correctly', async () => { const api = apiService(); //naming does not make it clear it is for mocking //..rest of test }); }); """ ### 3.3. Avoiding Over-Abstraction * **Standard:** Avoid creating overly complex or abstract test components that are difficult to understand and use. * **Why:** Simplicity and clarity are key in testing. Over-abstraction can make tests harder to debug and maintain. * **Do This:** Keep your test components focused and easy to understand. If a component becomes too complex, consider breaking it down into smaller parts. * **Don't Do This:** Create deeply nested inheritance hierarchies or overly generic test components. ### 3.4. Component Updates with Refactoring * **Standard:** Regularly review and refactor your test components to keep them aligned with the latest best practices and the evolving codebase. * **Why:** Prevents test components from becoming outdated or brittle, ensuring they remain effective and maintainable. * **Do This:** Schedule regular code reviews and refactoring sessions specifically for your test codebase. Update your components as Vitest itself releases updates. * **Don't Do This:** Neglect your test codebase and allow it to stagnate. ## 4. Advanced Component Design Patterns In Vitest This section will cover more advanced patterns when creating test components. ### 4.1. Dependency Injection for Testability * **Standard:** Design components to facilitate dependency injection, making it easier to mock or stub dependencies during testing. * **Why:** Allows you to isolate the unit under test and control its dependencies, creating more reliable and focused unit tests. * **Do This:** Pass dependencies as arguments to your component's constructor or functions. Use Vitest's mocking capabilities (e.g., "vi.mock", "vi.spyOn") to replace dependencies with mock implementations. * **Don't Do This:** Hardcode dependencies within your components, making them difficult to test in isolation. """typescript // Good: Dependency Injection import { describe, it, expect, vi } from 'vitest'; const fetchData = async (apiClient) => { const response = await apiClient.getData(); return response.data; }; describe('fetchData', () => { it('should fetch data correctly', async () => { const mockApiClient = { getData: vi.fn().mockResolvedValue({ data: [{ id: 1, name: 'Item 1' }] }), }; const data = await fetchData(mockApiClient); expect(data).toEqual([{ id: 1, name: 'Item 1' }]); expect(mockApiClient.getData).toHaveBeenCalled(); }); }); // Bad: Hardcoded Dependency, making testing difficult. const fetchDataBad = async () => { const apiClient = { //Real Implementation getData: async () => { return { data: [{ id: 1, name: 'Item 1' }] }; } }; const response = await apiClient.getData(); return response.data; }; describe('fetchDataBad', () => { //Hard to isolate API calls for testing it.skip('should fetch data correctly (Hard to test)', async () => { const data = await fetchDataBad(); expect(data).toEqual([{ id: 1, name: 'Item 1' }]); }); }); """ ### 4.2. State Management Patterns (e.g., Redux, Vuex Pinia) * **Standard:** When testing components that interact with state management libraries, create dedicated test components to manage the state and mock store interactions. * **Why:** Simplifies testing complex stateful components and ensures that state transitions are handled correctly. * **Do This:** Create mock store instances or specialized test reducers to isolate the component under test. Use libraries like "@vue/test-utils" or "@reduxjs/toolkit" to simplify state management testing. * **Don't Do This:** Directly manipulate the global store within your component tests. ### 4.3 Mocking Strategies with "vi" * **Standard:** Employ the "vi" object (from Vitest) judiciously for creating mocks, stubs, and spies to isolate units of code and control their behavior during testing. * **Why:** Facilitates focused testing of individual components by replacing real dependencies with controlled substitutes, ensuring predictable test outcomes. * **Do This:** Utilize "vi.fn()" to create mock functions, "vi.spyOn()" to observe method calls on existing objects, and "vi.mock()" to replace entire modules with mock implementations. * **Don't Do This:** Overuse mocking, which can lead to brittle tests that are tightly coupled to implementation details. Strive for a balance between isolation and integration testing. """typescript // Mocking Strategies with vi import { describe, it, expect, vi } from 'vitest'; describe('MyComponent', () => { it('should call the API service on mount', () => { const apiService = { fetchData: vi.fn().mockResolvedValue([{ id: 1, name: 'Item 1' }]), }; // Simulate component using the API Service. const component = { mounted: () => { apiService.fetchData(); }, }; component.mounted(); expect(apiService.fetchData).toHaveBeenCalled(); }); it('should update the component state with the fetched data', async () => { const apiService = { fetchData: vi.fn().mockResolvedValue([{ id: 1, name: 'Item 1' }]), }; // Simulate component using the API Service. const component = { data: null, mounted: async () => { component.data = await apiService.fetchData(); }, }; await component.mounted(); expect(component.data).toEqual([{ id: 1, name: 'Item 1' }]); }); }); """ By following these component design standards, you can create a robust, maintainable, and efficient test suite for Vitest. This will lead to higher-quality software and a more productive development process.