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Jest is a powerful JavaScript testing framework designed for simplicity and performance. Stark.ai offers a curated collection of Jest interview questions, real-world scenarios, and expert guidance to help you excel in your next technical interview.
Jest is a JavaScript testing framework developed by Facebook that focuses on simplicity. Key features include: 1)...
Jest setup involves: 1) Installing Jest using npm/yarn: 'npm install --save-dev jest', 2) Adding test script to...
A Jest test consists of: 1) describe blocks for grouping related tests, 2) it or test blocks for individual test...
Matchers are methods that let you test values in different ways. Common matchers include: 1) toBe() for exact...
Async testing can be handled through: 1) Returning promises: return promise.then(), 2) Async/await: async () => {...
Jest provides lifecycle hooks: 1) beforeAll() - runs once before all tests, 2) beforeEach() - runs before each test,...
Jest provides multiple mocking approaches: 1) jest.fn() for function mocking, 2) jest.mock() for module mocking, 3)...
Snapshot testing: 1) Captures component/data structure output, 2) Saves as reference file, 3) Compares against...
Test isolation involves: 1) Using beforeEach/afterEach for setup/cleanup, 2) Avoiding shared state between tests, 3)...
Code coverage measures how much code is tested. Jest configuration: 1) Add --coverage flag to test command, 2)...
jest.fn() creates a mock function that allows: 1) Tracking calls and arguments, 2) Setting return values using...
jest.spyOn() is used to: 1) Monitor method calls on objects, 2) Preserve original implementation while tracking...
Key differences: 1) jest.fn() creates new mock functions while spyOn monitors existing ones, 2) spyOn can restore...
Module mocking uses: 1) jest.mock() for automatic mocking, 2) Manual mocks in __mocks__ directory, 3)...
Mock return values can be set using: 1) mockReturnValue() for fixed values, 2) mockReturnValueOnce() for single...
Mock calls verified using: 1) toHaveBeenCalled() for call checking, 2) toHaveBeenCalledWith() for argument checking,...
mockClear(): 1) Resets call history of mock function, 2) Used between tests to ensure isolation, 3) Doesn't reset...
Async mocking involves: 1) mockResolvedValue() for successful promises, 2) mockRejectedValue() for failed promises,...
Manual mocks: 1) Created in __mocks__ directory, 2) Match module name and structure, 3) Exported as module.exports,...
ES6 class mocking: 1) Use jest.mock() for class, 2) Mock constructor and methods, 3) Implement instance methods with...
expect is Jest's assertion function that: 1) Takes a value to test, 2) Returns an expectation object, 3) Chains with...
Key differences: 1) toBe() uses Object.is for strict equality, 2) toEqual() performs deep equality comparison, 3)...
Truthiness matchers include: 1) toBeTruthy() - checks if value is truthy, 2) toBeFalsy() - checks if value is falsy,...
Numeric matchers include: 1) toBeGreaterThan(), 2) toBeLessThan(), 3) toBeGreaterThanOrEqual(), 4)...
String matchers include: 1) toMatch() for regex patterns, 2) toContain() for substring checks, 3) toHaveLength() for...
Array matchers include: 1) toContain() for item presence, 2) toHaveLength() for array length, 3) toEqual() for deep...
Object matchers include: 1) toEqual() for deep equality, 2) toMatchObject() for partial matching, 3)...
Exception testing uses: 1) toThrow() for any error, 2) toThrowError() with specific error, 3) expect(() =>...
The not modifier: 1) Inverts matcher expectation, 2) Used as .not before matchers, 3) Works with all matchers, 4)...
Promise testing uses: 1) resolves matcher for success, 2) rejects matcher for failures, 3) Async/await syntax, 4)...
Jest initialization involves: 1) Installing Jest: npm install --save-dev jest, 2) Adding test script to...
jest.config.js is the main configuration file that includes: 1) testEnvironment setting, 2) moduleFileExtensions, 3)...
Test environment configuration includes: 1) Setting testEnvironment in config (jsdom/node), 2) Creating custom...
Transform configs handle: 1) File preprocessing before tests, 2) Babel integration for modern JavaScript, 3)...
Test pattern configuration uses: 1) testMatch for glob patterns, 2) testRegex for regex patterns, 3)...
setupFilesAfterEnv: 1) Runs setup code after test framework initialization, 2) Configures global test setup, 3) Adds...
Coverage configuration includes: 1) collectCoverage flag, 2) coverageDirectory setting, 3) coverageThreshold...
Module mappings use: 1) moduleNameMapper in config, 2) Alias definitions, 3) Regular expression patterns, 4)...
Timeout configuration includes: 1) Global testTimeout setting, 2) Individual test timeouts, 3) Async operation...
Globals configuration: 1) Define global variables, 2) Set up global mocks, 3) Configure global setup/teardown, 4)...
React Testing Library: 1) Works with Jest as test runner, 2) Provides utilities for testing React components, 3)...
Component rendering tests: 1) Use render function from Testing Library, 2) Query rendered elements, 3) Assert on...
Query types include: 1) getBy* for elements that should be present, 2) queryBy* for elements that might not exist,...
User event testing: 1) Import userEvent from @testing-library/user-event, 2) Simulate user interactions, 3) Assert...
jest-dom provides: 1) DOM-specific matchers, 2) toBeInTheDocument(), 3) toHaveClass(), 4) toBeVisible(), 5)...
Props testing includes: 1) Rendering with different prop values, 2) Testing prop type validation, 3) Verifying prop...
Form testing involves: 1) Input change simulation, 2) Form submission testing, 3) Validation testing, 4) Error...
Hook testing requires: 1) @testing-library/react-hooks, 2) renderHook utility, 3) Testing state updates, 4) Testing...
Accessibility testing includes: 1) Role-based queries, 2) ARIA attribute testing, 3) Keyboard navigation testing, 4)...
State testing involves: 1) Triggering state updates, 2) Verifying state changes, 3) Testing state-dependent...
Integration testing: 1) Tests interactions between components/modules, 2) Verifies combined functionality, 3) Tests...
Setup includes: 1) Configuring test environment, 2) Setting up test databases/services, 3) Creating test fixtures,...
Common patterns: 1) Component interaction testing, 2) API integration testing, 3) Database integration testing, 4)...
Test data handling: 1) Setup test databases, 2) Create seed data, 3) Manage test data isolation, 4) Clean up after...
Mocking in integration tests: 1) Mock external services selectively, 2) Keep core integrations real, 3) Mock...
API integration testing: 1) Test real API endpoints, 2) Verify request/response handling, 3) Test error scenarios,...
Database testing practices: 1) Use test database instance, 2) Reset database state between tests, 3) Test...
Test isolation involves: 1) Independent test databases, 2) Cleaning up test data, 3) Resetting state between tests,...
Service testing strategies: 1) Test service communication, 2) Verify service contracts, 3) Test service...
Async handling: 1) Use async/await syntax, 2) Set appropriate timeouts, 3) Handle promise chains, 4) Test concurrent...
Measuring execution time: 1) Use jest.useFakeTimers(), 2) Use console.time/timeEnd, 3) Implement custom timing...
Test timeout configuration: 1) Set global timeout in config, 2) Set individual test timeouts, 3) Balance timeout vs...
Identifying slow tests: 1) Use --verbose flag, 2) Implement custom timing reporters, 3) Monitor test execution...
Basic metrics include: 1) Test execution time, 2) Setup/teardown time, 3) Memory usage, 4) Number of assertions, 5)...
Async performance testing: 1) Measure async operation duration, 2) Track concurrent operations, 3) Monitor resource...
Parallelization impacts: 1) Reduced total execution time, 2) Increased resource usage, 3) Potential test...
Memory measurement: 1) Use process.memoryUsage(), 2) Track heap snapshots, 3) Monitor garbage collection, 4) Measure...
Common bottlenecks: 1) Large test setups, 2) Excessive mocking, 3) Unnecessary test repetition, 4) Poor test...
Optimization strategies: 1) Use beforeAll when possible, 2) Minimize per-test setup, 3) Implement efficient cleanup,...
Caching impacts: 1) Test result caching, 2) Module caching, 3) Transform caching, 4) Resource caching, 5) Cache...
Key principles include: 1) Test isolation - each test should be independent, 2) Clear test descriptions, 3) Single...
AAA pattern involves: 1) Arrange - setup test data and conditions, 2) Act - perform the action being tested, 3)...
Test organization best practices: 1) Keep tests close to source files, 2) Use consistent naming conventions...
Good test descriptions: 1) Clearly state what's being tested, 2) Describe expected behavior, 3) Use consistent...
Test data management: 1) Use fixtures for consistent data, 2) Implement factory functions, 3) Clean up test data...
Mock best practices: 1) Only mock what's necessary, 2) Keep mocks simple, 3) Clean up mocks after tests, 4) Use...
Assertion best practices: 1) Use specific assertions, 2) Keep assertions focused, 3) Use meaningful error messages,...
Hook guidelines: 1) Use beforeAll for one-time setup, 2) Use beforeEach for per-test setup, 3) Clean up resources in...
Error testing practices: 1) Test expected error conditions, 2) Verify error messages and types, 3) Test error...
Maintenance practices: 1) Regular test cleanup, 2) Update tests with code changes, 3) Remove obsolete tests, 4)...
Jest is a JavaScript testing framework developed by Facebook that focuses on simplicity. Key features include: 1) Zero config setup for most JavaScript projects, 2) Snapshot testing, 3) Built-in code coverage reports, 4) Isolated test execution, 5) Interactive mode for test development, 6) Powerful mocking system, 7) Support for async testing.
Jest setup involves: 1) Installing Jest using npm/yarn: 'npm install --save-dev jest', 2) Adding test script to package.json: { 'scripts': { 'test': 'jest' } }, 3) Creating test files with .test.js or .spec.js extensions, 4) Configuring Jest through jest.config.js if needed, 5) Setting up any required environment configurations.
A Jest test consists of: 1) describe blocks for grouping related tests, 2) it or test blocks for individual test cases, 3) expect statements for assertions. Example: describe('MyFunction', () => { it('should return correct value', () => { expect(myFunction()).toBe(true); }); });
Matchers are methods that let you test values in different ways. Common matchers include: 1) toBe() for exact equality, 2) toEqual() for deep equality, 3) toContain() for arrays/iterables, 4) toBeTruthy()/toBeFalsy() for boolean checks, 5) toMatch() for regex. Used with expect(): expect(value).matcher()
Async testing can be handled through: 1) Returning promises: return promise.then(), 2) Async/await: async () => { await result }, 3) Done callback: (done) => { process.then(done) }, 4) Resolves/rejects matchers: expect(promise).resolves.toBe(). Always ensure async operations complete before test ends.
Jest provides lifecycle hooks: 1) beforeAll() - runs once before all tests, 2) beforeEach() - runs before each test, 3) afterEach() - runs after each test, 4) afterAll() - runs once after all tests. Used for setup/cleanup operations. Example: setting up database connections, cleaning test data.
Jest provides multiple mocking approaches: 1) jest.fn() for function mocking, 2) jest.mock() for module mocking, 3) jest.spyOn() for monitoring function calls, 4) Manual mocks using __mocks__ directory, 5) Automatic mocking of node_modules. Mocks help isolate code for testing.
Snapshot testing: 1) Captures component/data structure output, 2) Saves as reference file, 3) Compares against future changes, 4) Helps detect unintended changes. Example: expect(component).toMatchSnapshot(). Useful for UI components and serializable data.
Test isolation involves: 1) Using beforeEach/afterEach for setup/cleanup, 2) Avoiding shared state between tests, 3) Mocking external dependencies, 4) Using describe blocks for context separation, 5) Resetting mocks between tests using jest.clearAllMocks().
Code coverage measures how much code is tested. Jest configuration: 1) Add --coverage flag to test command, 2) Configure coverage settings in jest.config.js, 3) Set coverage thresholds, 4) Specify files to include/exclude, 5) Generate coverage reports in different formats.
jest.fn() creates a mock function that allows: 1) Tracking calls and arguments, 2) Setting return values using mockReturnValue(), 3) Implementing custom behavior using mockImplementation(), 4) Clearing/resetting mock data, 5) Verifying call conditions. Example: const mock = jest.fn().mockReturnValue('result');
jest.spyOn() is used to: 1) Monitor method calls on objects, 2) Preserve original implementation while tracking calls, 3) Temporarily mock method behavior, 4) Restore original implementation using mockRestore(), 5) Access call history and mock functionality. Example: jest.spyOn(object, 'method')
Key differences: 1) jest.fn() creates new mock functions while spyOn monitors existing ones, 2) spyOn can restore original implementation, jest.fn() cannot, 3) spyOn requires an object and method, jest.fn() is standalone, 4) spyOn preserves original method by default, 5) jest.fn() starts as empty function.
Module mocking uses: 1) jest.mock() for automatic mocking, 2) Manual mocks in __mocks__ directory, 3) mockImplementation() for custom behavior, 4) requireActual() for partial mocking, 5) hoisting of jest.mock() calls. Example: jest.mock('./module', () => ({ method: jest.fn() }));
Mock return values can be set using: 1) mockReturnValue() for fixed values, 2) mockReturnValueOnce() for single calls, 3) mockImplementation() for custom logic, 4) mockResolvedValue() for promises, 5) mockRejectedValue() for promise rejections. Example: mock.mockReturnValue('result');
Mock calls verified using: 1) toHaveBeenCalled() for call checking, 2) toHaveBeenCalledWith() for argument checking, 3) toHaveBeenCalledTimes() for call count, 4) mock.calls array for detailed inspection, 5) mock.results for return values. Example: expect(mock).toHaveBeenCalledWith(arg);
mockClear(): 1) Resets call history of mock function, 2) Used between tests to ensure isolation, 3) Doesn't reset implementation or return values, 4) Often used in beforeEach, 5) Helps prevent test interdependence. Example: beforeEach(() => { mock.mockClear(); });
Async mocking involves: 1) mockResolvedValue() for successful promises, 2) mockRejectedValue() for failed promises, 3) mockImplementation() with async functions, 4) Chain .then handlers for complex cases, 5) Await mock function calls in tests. Example: mock.mockResolvedValue('result');
Manual mocks: 1) Created in __mocks__ directory, 2) Match module name and structure, 3) Exported as module.exports, 4) Can include complex implementations, 5) Automatically used when module is required. Used for consistent mock implementations across tests.
ES6 class mocking: 1) Use jest.mock() for class, 2) Mock constructor and methods, 3) Implement instance methods with mockImplementation, 4) Mock static methods directly, 5) Handle inheritance if needed. Example: jest.mock('./MyClass', () => { return jest.fn().mockImplementation(() => { return {method: jest.fn()}; }); });
expect is Jest's assertion function that: 1) Takes a value to test, 2) Returns an expectation object, 3) Chains with matchers (toBe, toEqual, etc.), 4) Supports async assertions, 5) Can be extended with custom matchers. Example: expect(value).toBe(expected);
Key differences: 1) toBe() uses Object.is for strict equality, 2) toEqual() performs deep equality comparison, 3) toBe() is for primitives and object references, 4) toEqual() is for object/array content comparison, 5) toEqual() recursively checks nested structures.
Truthiness matchers include: 1) toBeTruthy() - checks if value is truthy, 2) toBeFalsy() - checks if value is falsy, 3) toBeNull() - checks for null, 4) toBeUndefined() - checks for undefined, 5) toBeDefined() - checks if value is not undefined.
Numeric matchers include: 1) toBeGreaterThan(), 2) toBeLessThan(), 3) toBeGreaterThanOrEqual(), 4) toBeLessThanOrEqual(), 5) toBeCloseTo() for floating point. Example: expect(value).toBeGreaterThan(3);
String matchers include: 1) toMatch() for regex patterns, 2) toContain() for substring checks, 3) toHaveLength() for string length, 4) toEqual() for exact matches, 5) toString() for string conversion checks. Example: expect(string).toMatch(/pattern/);
Array matchers include: 1) toContain() for item presence, 2) toHaveLength() for array length, 3) toEqual() for deep equality, 4) arrayContaining() for partial matches, 5) toContainEqual() for object matching in arrays.
Object matchers include: 1) toEqual() for deep equality, 2) toMatchObject() for partial matching, 3) toHaveProperty() for property checks, 4) objectContaining() for subset matching, 5) toBeInstanceOf() for type checking.
Exception testing uses: 1) toThrow() for any error, 2) toThrowError() with specific error, 3) expect(() => {}).toThrow() syntax, 4) Error message matching, 5) Error type checking. Example: expect(() => fn()).toThrow('error message');
The not modifier: 1) Inverts matcher expectation, 2) Used as .not before matchers, 3) Works with all matchers, 4) Maintains proper error messages, 5) Useful for negative assertions. Example: expect(value).not.toBe(3);
Promise testing uses: 1) resolves matcher for success, 2) rejects matcher for failures, 3) Async/await syntax, 4) Return promises in tests, 5) Chain additional matchers. Example: expect(promise).resolves.toBe(value);
Jest initialization involves: 1) Installing Jest: npm install --save-dev jest, 2) Adding test script to package.json: { 'scripts': { 'test': 'jest' } }, 3) Creating jest.config.js (optional), 4) Setting up test directories, 5) Configuring environment if needed.
jest.config.js is the main configuration file that includes: 1) testEnvironment setting, 2) moduleFileExtensions, 3) setupFilesAfterEnv for setup files, 4) testMatch for test file patterns, 5) coverageThreshold settings, 6) transform configurations for preprocessors.
Test environment configuration includes: 1) Setting testEnvironment in config (jsdom/node), 2) Creating custom environments, 3) Configuring environment variables, 4) Setting up global mocks, 5) Handling environment-specific setup.
Transform configs handle: 1) File preprocessing before tests, 2) Babel integration for modern JavaScript, 3) TypeScript transformation, 4) Custom transformers for specific files, 5) Cache configuration for transforms.
Test pattern configuration uses: 1) testMatch for glob patterns, 2) testRegex for regex patterns, 3) testPathIgnorePatterns for exclusions, 4) File naming conventions (.test.js, .spec.js), 5) Directory organization patterns.
setupFilesAfterEnv: 1) Runs setup code after test framework initialization, 2) Configures global test setup, 3) Adds custom matchers, 4) Sets up test environment, 5) Configures global mocks. Example: ['./jest.setup.js']
Coverage configuration includes: 1) collectCoverage flag, 2) coverageDirectory setting, 3) coverageThreshold requirements, 4) collectCoverageFrom patterns, 5) coverageReporters options for report formats.
Module mappings use: 1) moduleNameMapper in config, 2) Alias definitions, 3) Regular expression patterns, 4) Identity-obj-proxy for style imports, 5) Custom module resolvers. Helps with import resolution and mocking.
Timeout configuration includes: 1) Global testTimeout setting, 2) Individual test timeouts, 3) Async operation timeouts, 4) Setup/teardown timeouts, 5) Custom timeout messages. Default is usually 5000ms.
Globals configuration: 1) Define global variables, 2) Set up global mocks, 3) Configure global setup/teardown, 4) Define global matchers, 5) Set up global test utilities. Available throughout test suite.
React Testing Library: 1) Works with Jest as test runner, 2) Provides utilities for testing React components, 3) Focuses on testing behavior over implementation, 4) Encourages accessibility-first testing, 5) Uses queries to find elements. Example: render(<Component />); expect(screen.getByText('text')).toBeInTheDocument();
Component rendering tests: 1) Use render function from Testing Library, 2) Query rendered elements, 3) Assert on element presence, 4) Check component content, 5) Verify proper props rendering. Example: const { getByText } = render(<Component prop={value} />);
Query types include: 1) getBy* for elements that should be present, 2) queryBy* for elements that might not exist, 3) findBy* for async elements, 4) getAllBy*, queryAllBy*, findAllBy* for multiple elements, 5) Role-based, text-based, and label-based queries.
User event testing: 1) Import userEvent from @testing-library/user-event, 2) Simulate user interactions, 3) Assert on resulting changes, 4) Handle async events, 5) Test form interactions. Example: await userEvent.click(button); expect(result).toBeVisible();
jest-dom provides: 1) DOM-specific matchers, 2) toBeInTheDocument(), 3) toHaveClass(), 4) toBeVisible(), 5) toHaveValue() and other UI-specific assertions. Enhances Jest for DOM testing.
Props testing includes: 1) Rendering with different prop values, 2) Testing prop type validation, 3) Verifying prop updates, 4) Testing default props, 5) Testing required props. Example: render(<Component testProp='value' />);
Form testing involves: 1) Input change simulation, 2) Form submission testing, 3) Validation testing, 4) Error message verification, 5) Form state testing. Use userEvent for input interactions.
Hook testing requires: 1) @testing-library/react-hooks, 2) renderHook utility, 3) Testing state updates, 4) Testing hook effects, 5) Testing custom hook logic. Example: const { result } = renderHook(() => useCustomHook());
Accessibility testing includes: 1) Role-based queries, 2) ARIA attribute testing, 3) Keyboard navigation testing, 4) Screen reader compatibility, 5) Color contrast verification. Ensures inclusive user experience.
State testing involves: 1) Triggering state updates, 2) Verifying state changes, 3) Testing state-dependent rendering, 4) Testing state transitions, 5) Async state updates. Focus on behavior over implementation.
Integration testing: 1) Tests interactions between components/modules, 2) Verifies combined functionality, 3) Tests real dependencies (vs mocked in unit tests), 4) Focuses on component communication, 5) Tests larger parts of the application together. More comprehensive but slower than unit tests.
Setup includes: 1) Configuring test environment, 2) Setting up test databases/services, 3) Creating test fixtures, 4) Configuring global setup/teardown, 5) Setting appropriate timeouts. Example: setupFilesAfterEnv for global setup.
Common patterns: 1) Component interaction testing, 2) API integration testing, 3) Database integration testing, 4) Service integration testing, 5) End-to-end flows. Focus on testing interfaces between parts.
Test data handling: 1) Setup test databases, 2) Create seed data, 3) Manage test data isolation, 4) Clean up after tests, 5) Use realistic test data. Important for meaningful integration tests.
Mocking in integration tests: 1) Mock external services selectively, 2) Keep core integrations real, 3) Mock non-essential dependencies, 4) Use realistic mock data, 5) Balance between isolation and realism.
API integration testing: 1) Test real API endpoints, 2) Verify request/response handling, 3) Test error scenarios, 4) Check authentication/authorization, 5) Test API versioning. Use actual HTTP calls.
Database testing practices: 1) Use test database instance, 2) Reset database state between tests, 3) Test transactions and rollbacks, 4) Verify data integrity, 5) Test database migrations.
Test isolation involves: 1) Independent test databases, 2) Cleaning up test data, 3) Resetting state between tests, 4) Isolating external services, 5) Managing shared resources. Prevents test interference.
Service testing strategies: 1) Test service communication, 2) Verify service contracts, 3) Test service dependencies, 4) Check error handling, 5) Test service state management.
Async handling: 1) Use async/await syntax, 2) Set appropriate timeouts, 3) Handle promise chains, 4) Test concurrent operations, 5) Verify async state changes. Important for realistic testing.
Measuring execution time: 1) Use jest.useFakeTimers(), 2) Use console.time/timeEnd, 3) Implement custom timing decorators, 4) Use performance.now(), 5) Configure Jest's verbose timing option. Example: const start = performance.now(); /* test */ const duration = performance.now() - start;
Test timeout configuration: 1) Set global timeout in config, 2) Set individual test timeouts, 3) Balance timeout vs expected performance, 4) Handle slow tests appropriately, 5) Monitor timeout failures for performance issues.
Identifying slow tests: 1) Use --verbose flag, 2) Implement custom timing reporters, 3) Monitor test execution times, 4) Set timing thresholds, 5) Use test profiling tools. Helps optimize test suite performance.
Basic metrics include: 1) Test execution time, 2) Setup/teardown time, 3) Memory usage, 4) Number of assertions, 5) Test suite duration. Important for establishing baselines.
Async performance testing: 1) Measure async operation duration, 2) Track concurrent operations, 3) Monitor resource usage, 4) Test throughput capabilities, 5) Handle timeouts appropriately.
Parallelization impacts: 1) Reduced total execution time, 2) Increased resource usage, 3) Potential test interference, 4) Worker process management, 5) Load balancing considerations.
Memory measurement: 1) Use process.memoryUsage(), 2) Track heap snapshots, 3) Monitor garbage collection, 4) Measure memory leaks, 5) Implement memory thresholds.
Common bottlenecks: 1) Large test setups, 2) Excessive mocking, 3) Unnecessary test repetition, 4) Poor test isolation, 5) Inefficient assertions. Identify and optimize these areas.
Optimization strategies: 1) Use beforeAll when possible, 2) Minimize per-test setup, 3) Implement efficient cleanup, 4) Share setup where appropriate, 5) Cache test resources.
Caching impacts: 1) Test result caching, 2) Module caching, 3) Transform caching, 4) Resource caching, 5) Cache invalidation strategies. Proper caching improves performance.
Key principles include: 1) Test isolation - each test should be independent, 2) Clear test descriptions, 3) Single assertion per test when possible, 4) Proper setup and cleanup, 5) Following the Arrange-Act-Assert pattern, 6) Testing behavior not implementation, 7) Maintaining test readability.
AAA pattern involves: 1) Arrange - setup test data and conditions, 2) Act - perform the action being tested, 3) Assert - verify the expected outcome. Important for: test clarity, maintainability, and proper organization of test logic.
Test organization best practices: 1) Keep tests close to source files, 2) Use consistent naming conventions (.test.js, .spec.js), 3) Group related tests in describe blocks, 4) Organize by feature or component, 5) Maintain clear file structure.
Good test descriptions: 1) Clearly state what's being tested, 2) Describe expected behavior, 3) Use consistent terminology, 4) Follow 'it should...' pattern, 5) Are specific and unambiguous. Helps with test documentation and maintenance.
Test data management: 1) Use fixtures for consistent data, 2) Implement factory functions, 3) Clean up test data after use, 4) Keep test data minimal and focused, 5) Avoid sharing mutable test data between tests.
Mock best practices: 1) Only mock what's necessary, 2) Keep mocks simple, 3) Clean up mocks after tests, 4) Use meaningful mock implementations, 5) Avoid mocking everything. Mocks should be minimal and focused.
Assertion best practices: 1) Use specific assertions, 2) Keep assertions focused, 3) Use meaningful error messages, 4) Avoid multiple assertions when possible, 5) Test one concept per test case.
Hook guidelines: 1) Use beforeAll for one-time setup, 2) Use beforeEach for per-test setup, 3) Clean up resources in afterEach/afterAll, 4) Keep hooks focused and minimal, 5) Avoid complex logic in hooks.
Error testing practices: 1) Test expected error conditions, 2) Verify error messages and types, 3) Test error handling behavior, 4) Use proper error assertions, 5) Consider edge cases and invalid inputs.
Maintenance practices: 1) Regular test cleanup, 2) Update tests with code changes, 3) Remove obsolete tests, 4) Maintain test documentation, 5) Refactor tests when needed. Keep tests current and valuable.
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