Interview Questions
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.
TypeScript configuration includes: 1) Installing ts-jest, 2) Configuring transform with ts-jest, 3) Setting up tsconfig.json, 4) Configuring type checking, 5) Handling TypeScript paths and aliases.
Platform configuration involves: 1) Environment-specific configs, 2) Conditional setup logic, 3) Platform-specific mocks, 4) Environment detection, 5) Platform-specific test runners.
Reporter configuration includes: 1) Custom reporter implementation, 2) Reporter options setup, 3) Multiple reporter configuration, 4) Output formatting, 5) Integration with CI/CD systems.
Test data configuration: 1) Fixture setup locations, 2) Data loading strategies, 3) Cleanup mechanisms, 4) Data isolation approaches, 5) Shared test data management.
Snapshot configuration: 1) snapshotSerializers setup, 2) Snapshot directory location, 3) Update and retention policies, 4) Custom serializers, 5) Snapshot format options.
Parallelization config includes: 1) maxWorkers setting, 2) Worker pool configuration, 3) Test file distribution, 4) Resource allocation, 5) Parallel run coordination.
Custom matcher configuration: 1) Matcher implementation, 2) Global matcher registration, 3) TypeScript definitions, 4) Matcher error messages, 5) Matcher documentation.
Test filtering config: 1) testNamePattern settings, 2) Test file patterns, 3) Tag-based filtering, 4) Run group configuration, 5) Conditional test execution.
Retry configuration: 1) jest-retry setup, 2) Retry attempts settings, 3) Retry delay configuration, 4) Failure conditions, 5) Retry reporting options.
Isolation configuration: 1) Test environment isolation, 2) State reset mechanisms, 3) Module isolation, 4) Database isolation, 5) Resource cleanup strategies.
Advanced environment config: 1) Custom environment implementation, 2) Environment chains, 3) Dynamic environment setup, 4) Environment state management, 5) Environment cleanup strategies.
Complex suite configuration: 1) Multi-project setup, 2) Shared configurations, 3) Dynamic config generation, 4) Configuration inheritance, 5) Project-specific overrides.
Custom runner implementation: 1) Runner API implementation, 2) Test execution flow, 3) Result reporting, 4) Resource management, 5) Integration with Jest infrastructure.
Monitoring configuration: 1) Metric collection setup, 2) Performance monitoring, 3) Resource tracking, 4) Alert configuration, 5) Monitoring integration points.
Advanced coverage config: 1) Custom coverage reporters, 2) Coverage analysis tools, 3) Branch coverage requirements, 4) Coverage enforcement rules, 5) Coverage trend analysis.
Factory configuration: 1) Factory implementation patterns, 2) Data generation strategies, 3) Factory composition, 4) State management, 5) Factory cleanup mechanisms.
Scheduler implementation: 1) Test execution ordering, 2) Resource allocation, 3) Priority management, 4) Dependency resolution, 5) Schedule optimization.
Infrastructure configuration: 1) CI/CD integration, 2) Resource provisioning, 3) Environment management, 4) Scaling strategies, 5) Infrastructure monitoring.
Advanced mocking config: 1) Custom mock factories, 2) Mock state management, 3) Mock verification systems, 4) Mock cleanup strategies, 5) Mock interaction recording.