Test Anything JS

A Test-Anything-Protocol library for Node.js

npm install tap
tap test/*.js

Saving Failures, Running Changed Tests

Occasionally you’ll want to re-run just part of a test suite, for example, just to run the tests that failed in the previous run, or running tests for files in your application that have changed since the last run. There are a few ways to do this in node-tap.

Save Failures to a File

With the --save=<file> option, you can write all failed tests to a file. If that file exists, then only the tests in that file will be re-run.

For example, say that you have two tests foo.test.js and bar.test.js. When you run tap --save=tests.txt, it will run both files, because the file does not exist.

Let’s say that foo.test.js passes, but bar.test.js fails. At the end of the test run, bar.test.js will be written to the tests.txt file. So, if you run tap --save=tests.txt again, it will only run bar.test.js. When tap does this, it makes sure to keep the old coverage information around, and only delete the coverage information related to that test file, so that you don’t end up with corrupted coverage results.

The workflow, then goes like this:

Bail on first failure, then resume

One useful way to work through a project is to run with both a --save=file and with --bail. In this case, tap will bail out on the first failure, and any tests that were skipped will be put into the save file, so you can fix the failure, and then pick right back up where you were by running with tap --bail --save=file again.


If you run tap with --changed (or -n), it will only run tests if the test file, or any of the files it covers, have changed since the last run.

Because this depends on tracking which test covered which file, it requires that you have coverage enabled (which is on by default anyway).

Tip: Use a Coverage Map Module

If you specify a --coverage-map=<file> option, then you can be very precise about which files under test should trigger a re-run of the tests.