watch-mode.md

Watch mode

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AVA comes with an intelligent watch mode. It watches for files to change and runs just those tests that are affected.

Running tests with watch mode enabled

You can enable watch mode using the --watch or -w flags. If you have installed AVA globally:

$ ava --watch

If you've configured it in your package.json like this:

{
  "scripts": {
    "test": "ava"
  }
}

You can run:

$ npm test -- --watch

You could also set up a special script:

{
  "scripts": {
    "test": "ava",
    "test:watch": "ava --watch"
  }
}

And then use:

$ npm run test:watch

Requirements

AVA uses chokidar as the file watcher. It's configured as an optional dependency since chokidar sometimes can't be installed. Watch mode is not available if chokidar fails to install, instead you'll see a message like:

The optional dependency chokidar failed to install and is required for --watch. Chokidar is likely not supported on your platform.

Please refer to the chokidar documentation for how to resolve this problem.

Source files and test files

In AVA there's a distinction between source files and test files. As you can imagine the test files contain your tests. Source files are all other files that are needed for the tests to run, be it your source code or test fixtures.

By default AVA watches for changes to the test files, package.json, and any other .js files. It'll ignore files in certain directories as provided by the ignore-by-default package.

You can configure patterns for the source files using the --source CLI flag or in the ava section of your package.json file. Note that if you specify a negative pattern the directories from ignore-by-default will no longer be ignored, so you may want to repeat these in your config.

If your tests write to disk they may trigger the watcher to rerun your tests. If this occurs you will need to use the --source flag.

Dependency tracking

AVA tracks which source files your test files depend on. If you change such a dependency only the test file that depends on it will be rerun. AVA will rerun all tests if it cannot determine which test file depends on the changed source file.

Dependency tracking works for required modules. Custom extensions and transpilers are supported, provided you loaded them using the --require CLI flag and not from inside your test file. Files accessed using the fs module are not tracked.

Watch mode and the .only modifier

The .only modifier disables watch mode's dependency tracking algorithm. When a change is made, all .only tests will be rerun, regardless of whether the test depends on the changed file.

Manually rerunning all tests

You can quickly rerun all tests by typing r on the console, followed by Enter.

Debugging

Sometimes watch mode does something surprising like rerunning all tests when you thought only a single test would be run. To see its reasoning you can enable a debug mode:

$ DEBUG=ava:watcher npm test -- --watch

On Windows use:

$ set DEBUG=ava:watcher
$ npm test -- --watch

Help us make watch mode better

Watch mode is relatively new and there might be some rough edges. Please report any issues you encounter. Thanks!