jest-configuration

Configure Jest for TypeScript by setting up ts-jest as your transform, specifying moduleFileExtensions to include .ts and .tsx, and configuring testEnvironment based on your runtime. Use a jest.config.js or package.json jest field with appropriate roots and testMatch patterns to locate your test files.

For React testing-library projects, configure testEnvironment to jsdom, set up setupFilesAfterEnv to load testing-library matchers, use moduleNameMapper to handle CSS and asset imports, and configure transform for both JavaScript and TypeScript. Include collectCoverageFrom and coverageThreshold to enforce test coverage standards.

Configure Jest with projects array specifying roots and testMatch for each project, or use separate jest.config.js files per workspace. Set moduleFileExtensions, transform, and setupFilesAfterEnv consistently across projects to ensure reliable test execution and coverage collection across repositories.

Yes. Configure moduleFileExtensions with both .js and .ts extensions, set up transform to handle both file types using ts-jest or babel, and ensure testMatch patterns capture both .test.js and .test.ts files. This works for mixed-language projects and monorepos.

Use setupFilesAfterEnv to load matchers and global configuration after Jest environment initialization. Configure clearMocks and restoreMocks to control state between tests, and define custom matchers or extend built-in ones in setup files to ensure predictable test isolation and consistent assertions.

Check testMatch patterns, roots, and moduleFileExtensions match your project layout. Verify transform is configured for your file types, moduleNameMapper handles non-JS imports, and setupFilesAfterEnv paths are correct. Use verbose output to diagnose resolution and execution issues.