Run only ONE test with Jest

Question

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?

Answer 1

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.

Press p, and then type a filename.

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

Answer 2

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"

Answer 3

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

Answer 4

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

Answer 5

I created a command that makes Jest work like you (and I) expect. This is work in progress, but should work like this:

Run tests from files that have .only tests/describes or run all of them if there's no .only.

grep --exclude-dir=node_modules -rl . -e 'test.only\|it.only\|describe.only' --null | tr '\n' ' ' | xargs -0 npx jest | grep . || npx jest

Even if this does not work in some edge cases you can take it as a reference. I might keep this more up-to-date here.

You can create an alias for this, put it in a shell script or in a package.json script.

Update: The | grep . || npx jest at the end is a workaround because xargs should run once with no input, but it does not on my machine. Maybe it's not needed normally.

Answer 6

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

Answer 7

According to https://stackoverflow.com/a/44446669/3957754 .only is and will be ignored in jest

This worked for me, only for LINUX users:

• create a bash script
• using grep to find files containing the word "only"
• pass these files: jest foo.test.js bar.test.js

test.sh

filtered_test=$(grep -rnwl ./src/test -e "test.only\|it.only\|describe.only" --include \*.js | tr '\n' ' ')
jest --coverage --silent --runInBand --detectOpenHandles $filtered_test

package.json

"scripts": {
  "start": "...",
  "dev": "...",
  "test": "./src/test/test.sh"
},

Result: Only tests with only are executed

Note1: If your tests are not in src/test change that value in the bash script and package.json

Note2: Create simple npm module to do the same should be easy

Answer 8

A simple automated workaround is to use a bash script to create-and-run the jest command:

tools/runJest.sh

#!/bin/bash

function main() {
  local testDir="test"
  local testFiles="$(grep -rl '\.only(' $testDir | grep '\.test\.js$' | xargs)"

  if [ -z "$testFiles" ]; then
    runJest "--testPathPattern=test/unit"
  else
    runJest "$testFiles"
  fi
}

function runJest() {
  local testFiles="$1"
  local cmd="jest --logHeapUsage -c jest.config.js $testFiles"

  echo "Running cmd: $cmd"
  $cmd
}

main "$@"

What it does:

• find all test files that have .only( in them
• if there are .only( hits, run jest only on the files with hits
• otherwise, run regular jest config

Make sure to add executable permissions to the bash script

chmod +x tools/runJest.sh

Also modify the script's search criteria (folder, filename patterns) to your specific setup.

package.json scripts.test

Instead of

{
  "scripts": {
    "test": "jest --logHeapUsage --testPathPattern=test/unit -c jest.config.js"
  }
}

Do this:

{
  "scripts": {
    "test": "tools/runJest.sh"
  }
}