Testing a Single File with Jest: Encountering Errors

Product Support
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#1

How do I test a single file using Jest? I can run multiple test files using Jest, but I’m having trouble testing a single file. Here’s what I’ve done so far:

  1. Installed Jest CLI as a dev dependency: npm install jest-cli --save-dev.
  2. Updated package.json with the script: { … “scripts”: { “test”: “jest” } … }.
  3. Written multiple tests, and running npm test works and executes all tests.

However, I want to test a specific file, for example, app/foo/tests/bar.spec.js. When I try running: npm test app/foo/tests/bar.spec.js

from the project root, I encounter the following error:

npm ERR! Error: ENOENT, open ‘/node_modules/app/foo/tests/bar.spec.js/package.json’

How can I correctly run a specific test file using npm run test?

#2

Use Jest Command Directly: Instead of using npm run test with a file path, you can invoke Jest directly from the command line and specify the test file. From your project root, run:

npx jest app/foo/__tests__/bar.spec.js

This directly runs Jest with the specified file, bypassing the npm command. This method ensures that you can npm run test specific file without any issues.

#3

Modify the test Script in package.json: Update the test script in your package.json to accept arguments for specifying test files. Modify the scripts section as follows:

"scripts": {

"test": "jest"

}

Then run:

npm test -- app/foo/__tests__/bar.spec.js

The -- syntax tells npm to pass the following arguments directly to Jest. This way, you can easily npm run test specific file by appending the file path.

#4

Use Jest’s --testPathPattern Option: You can use Jest’s --testPathPattern option to specify the test file pattern. Run:


npx jest --testPathPattern=app/foo/__tests__/bar.spec.js

Or modify the test script in package.json to include this option:


"scripts": {

"test": "jest --testPathPattern"

}

Then run:


npm test app/foo/__tests__/bar.spec.js

This ensures that only the specified file(s) matching the pattern will be tested. It’s a reliable way to npm run test specific file seamlessly.