How do I test a single file using Jest?

To run an individual test:

npm test -t ValidationUtil # `ValidationUtil` is my module `ValidationUtil.spec.js`

-t - after it, put a regular expression containing the test name.

Since at least 2019:

npm test -- bar.spec.js

In 2015:

In order to run a specific test, you'll need to use the jest command. npm test will not work. To access jest directly on the command line, install it via npm i -g jest-cli or yarn global add jest-cli.

Then simply run your specific test with jest bar.spec.js.

Note: You don't have to enter the full path to your test file. The argument is interpreted as a regular expression. Any part of the full path that uniquely identifies a file suffices.

If you install the Visual Studio Code plugin Jest Runner,

You will have Debug/Run options above every describe and it.

You can open your test file in Visual Studio Code and click on one of those options.

All you have to do is chant the magic incantation:

npm test -- SomeTestFileToRun

The stand-alone -- is *nix magic for marking the end of options, meaning (for NPM) that everything after that is passed to the command being run, in this case jest. As an aside, you can display Jest usage notes by saying

npm test -- --help

Anyhow, chanting

npm test -- Foo

runs the tests in the named file (FooBar.js). You should note, though, that:

• Jest treats the name as case-sensitive, so if you're using a case-insensitive, but case-preserving file system (like Windows NTFS), you might encounter what appears to be oddness going on.

• Jest appears to treat the specification as a prefix.

So the above incantation will

• Run FooBar.js, Foo.js and FooZilla.js
• But not run foo.js