Jest

Coverage Commands

Measure test coverage with Jest's built-in Istanbul integration. Generate coverage reports, set thresholds, and identify untested code paths to improve test quality.

8 commands

Pro Tips

Run 'jest --coverage --coverageReporters=text' for a quick terminal summary without generating HTML files.

Set coverage thresholds in jest config to fail CI if coverage drops: 'coverageThreshold: { global: { branches: 80 } }'.

Use 'collectCoverageFrom' to include files that have no tests yet — reveals completely untested modules.

Common Mistakes

100% coverage doesn't mean bug-free code. Focus on testing behavior and edge cases, not just hitting lines.

Coverage collection slows tests significantly. Only enable '--coverage' in CI, not during local development.

Commands

CI mode

$ jest --ci

Run in continuous integration mode.

Bail on failure

$ jest --bail

Exit immediately on first test failure.

Coverage from pattern

$ jest --collectCoverageFrom='src/**/*.js'

Collect coverage from specific files.

Coverage directory

$ jest --coverageDirectory=coverage

Set coverage output directory.

Coverage reporters

$ jest --coverageReporters=html,text,lcov

Specify coverage report formats.

Tests since branch

$ jest --changedSince main

Run tests changed since git branch.

List all tests

$ jest --listTests

List all test files Jest will run.

Show configuration

$ jest --showConfig

Display resolved Jest configuration.