Run only ONE test with Jest

116
votes

I want to run just one test with Jest.

I use it.only or describe.only, but it still runs a whole lot of tests. I think it runs all the tests since my last commit, but it shouldn't have this behavior with the only flag explicitly set, right?

What causes this behavior and how can I run a single test?

5
javascriptunit-testingjestjs
Possible duplicate of How do I run a single test using Jest? - YPCrumble
If I accept the "duplicate flag" it "will mark your question as a duplicate, directing future readers to the original question and preventing further answers from being posted here." I don't think they are exactly the same, since the each question and answers are taking different approaches. - jpenna
@jpenna: just look at the original question. The same answers were given. - Dan Dascalescu

5 Answers

147
votes

Jest parallelizes test runs and it doesn't know upfront which tests it should run and which it shouldn't run. This means when you use "fit", it will only run one test in that file. But it still runs all other test files in your project.

fit, fdescribe and it.only, describe.only have the same purpose: skip other tests and run only me.

Source: https://github.com/facebook/jest/issues/698#issuecomment-177673281

Use the Jest filtering mechanism. When you run your tests like,

jest --config=jest.config.json --watch

you can filter tests by a testname or filename. Just follow the instructions in the terminal.

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Press p, and then type a filename.

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Then you can use describe.only and it.only which will skip all other tests from the filtered, tested file.

31
votes

it.only and describe.only work only for the module they are in. If you are having problems to filter tests in multiple files, you can use jest -t name-of-spec, filtering tests that match the specified name (match against the name in describe or test).

Source: Jest CLI Options

For example, I focus the test which I'm currently writing like this (with the test script in the package.json):
npm test -- -t "test foo"

13
votes

For me it works if I use two parameters like this:

yarn test --watch -f "src/...fullpath.../reducer.spec.js" -t "Name of the test"

Flags:

--watch: is optional

-f: will do filtering of your files, so if you have a lot of tests with the same name, specify the full path to the exact file

-t: works with 'describe' name or 'it' name of your test
11
votes

It's like this:

jest sometest.test.js -t "some expression to match a describe or a test"

It will test all files with the name sometest.test.js and matching based on -t option. If you only want to test a specific file, you can do this:

jest src/user/.../sometest.test.js
-1
votes

Trying to enter the full path results on 0 matches to that pattern, even though the file exists and has a couple of assertions.