Angular Unit Test Code Coverage with Karma

Angular CLI can run unit tests and create code coverage reports for your Angular projects. Coverage tells you which parts of your codebase your unit tests actually exercise — and, more usefully, which they don't.

You generate coverage with:

ng test --no-watch --code-coverage

The --no-watch flag matters: without it, Karma stays in watch mode and the report is only written when the process exits, which is why "my coverage folder is empty" is such a common complaint. In CI you always want --no-watch so the run completes and exits with a pass/fail status.

This creates a new /coverage folder in your project root. Add it to .gitignore — it's a build artefact.

You also need to add this option in angular.json:

"test": {
  "options": {
    "codeCoverage": true
  }
}
 

To set code coverage threshold you need to enable this in your Karma configuration file, karma.conf.js, by adding the check property in the coverageReporter:

coverageReporter: {
  check: {
    emitWarning: false,
    global: {
      statements: 50,
      branches: 50,
      functions: 50,
      lines: 50,
      excludes: [
        'app/bar/**/*.ts'
      ]
    },
    each: {
      statements: 50,
      branches: 50,
      functions: 50,
      lines: 50,
      excludes: [
        'app/directory/**/*.ts'
      ],
    }
  }
}
 

check is used to configure minimum threshold enforcement for coverage results. If the thresholds are not met, karma will fail the test.

Code Coverage Report

Code Coverage of a file

For more details please refer to this link - Angular

For Karma configuration details - Karma configuration

Related: see the Angular unit testing with Jasmine and Karma guide for how this fits with the rest of the toolchain.

Sources

• Angular docs