Is there a way to run some tests sequentially with Jest?

Question

Jest runs your test suite in parallel by default, but there is a flag (--runInBand) that allows you to run the whole suite sequentially (as pointed out here)

I have some tests that cannot run in parallel, but running the whole suite sequentially takes a lot longer in total, so my question is if there is way to only run some tests that way (such as setting a flag for those tests or something similar).

Answer 1

Extended from Joachim Lous's answer, you can divide test files into projects and specify a different runner for each project.

In jest.config.js:

const commonOptions = {
  // Common project options
  preset: "my-preset",
  roots: [
    '<rootDir>/src/',
  ],
  // …
};

module.exports = {

  // Global Jest options:
  verbose: true,
  testTimeout: 5_000,
  reporters: ['default'],

  // Project-specific options:
  projects: [
    {
      ...commonOptions,
      displayName: "parallel-tests",
      testMatch: ['**/*.test.js'],
    },
    {
      ...commonOptions,
      displayName: "serial-tests",
      runner: "jest-serial-runner", // <-- IMPORTANT
      testMatch: ['**/*.serial-test.js'],
    },
  ],

}

Then, rename any tests that need to be run sequentially to *.serial-test.js (as opposed to *.test.js).

Don't forget to install the jest-serial-runner package:

npm i -D jest-serial-runner

Answer 2

This was a bit of a lift, but I think it's worth posting my final config. I had this same problem and I extended Joachim Lous' and Fishball's answers to get to a satisfactory result. Here's my final setup:

An abbreviated directory listing of my project:

├── src
│   ├── index.ts
│   ├── Io.ts
│   ├── Modules
│   │   └── index.ts
│   └── .....
└── tests
    ├── EndToEnd
    │   ├── Fixtures.ts
    │   ├── Mq.spec.ts
    │   ├── LegalEntities.spec.ts
    │   └── Utils.ts
    └── UnitTests
        ├── LegalEntities.spec.ts
        ├── Assets.spec.ts
        └── Utils.ts

My (abbreviated) package.json file with my jest configs in it:

{
  "name": "my-project",
  "scripts": {
    "build": "scripts/build",
    "check": "tsc --noEmit",
    "test": "jest"
  },
  "....": "....",
  "jest": {
    "projects": [
      {
        "displayName": "unit-tests",
        "testEnvironment": "node",
        "verbose": true,
        "testMatch": [
          "<rootDir>/tests/**/*.spec.ts",
          "!**/EndToEnd/**/*.spec.ts"
        ],
        "transform": {
          "^.+\\.tsx?$": "ts-jest"
        }
      },
      {
        "displayName": "e2e-tests",
        "testEnvironment": "node",
        "verbose": true,
        "maxWorkers": 1,
        "testMatch": [
          "<rootDir>/tests/EndToEnd/**/*.spec.ts"   
        ],
        "transform": {
          "^.+\\.tsx?$": "ts-jest"
        }
      }
    ]
  }
}

Things to note:

• When using the projects key in jest, I had to move all config into the individual project blocks. Using project config was mutually-exclusive with using global config.
• I did not use the runner directive as mentioned in other answers. Instead I used the maxWorkers option to limit execution to 1 worker (i.e., inherently serial). This meant I didn't have to use more dependencies.
• For some reason the negation syntax was finicky with my unit tests. I wanted to specify unit tests as all tests that were NOT in the EndToEnd directory, and it took me a few tried to get jest to do this correctly.

Thanks to everyone else for the viable starting point. Hope this helps others!

Answer 3

Use the serial test runner:

npm install jest-serial-runner --save-dev

Set up jest to use it, e.g. in jest.config.js:

module.exports = {
   ...,
   runner: 'jest-serial-runner'
};

You can use the project feature to apply it only to a subset of tests. See https://jestjs.io/docs/en/configuration#projects-arraystring--projectconfig

Answer 4

I too needed the same functionality. I have a large set of Jest integration test suites I want to run. However, some can't be run in parallel due to the need of setup and teardown of a shared resource. So, here is the solution I came up with.

I updated my package.json scripts from:

{
  ...
  "scripts": {
    ...
    "test": "npm run test:unit && npm run test:integration",
    "test:integration": "jest --config=__tests__/integration/jest.config.js",
    "test:unit": "jest --config=__tests__/unit/jest.config.js"
  },
  ...
}

to

{
  ...
  "scripts": {
    ...
    "test": "npm run test:unit && npm run test:integration",
    "test:integration": "npm run test:integration:sequential && npm run test:integration:parallel",
    "test:integration:parallel": "jest --config=__tests__/integration/jest.config.js",
    "test:integration:sequential": "jest --config=__tests__/integration/jest.config.js --runInBand",
    "test:unit": "jest --config=__tests__/unit/jest.config.js"
  },
  ...
}

Then I updated __tests__/integration/jest.config.js from

module.exports = {
  // Note: rootDir is relative to the directory containing this file.
  rootDir: './src',
  setupFiles: [
    '../setup.js',
  ],
  testPathIgnorePatterns: [
    ...
  ],
};

to

const Path = require('path');

const { defaults } = require('jest-config');
const klawSync = require('klaw-sync')
const mm = require('micromatch');

// Note: rootDir is relative to the directory containing this file.
const rootDir = './src';
const { testMatch } = defaults;

// TODO: Add the paths to the test suites that need to be run
// sequentially to this array.
const sequentialTestPathMatchPatterns = [
  '<rootDir>/TestSuite1ToRunSequentially.spec.js',
  '<rootDir>/TestSuite2ToRunSequentially.spec.js',
  ...
];

const parallelTestPathIgnorePatterns = [
  ...
];

let testPathIgnorePatterns = [
  ...parallelTestPathIgnorePatterns,
  ...sequentialTestPathMatchPatterns,
];

const sequential = process.argv.includes('--runInBand');
if (sequential) {
  const absRootDir = Path.resolve(__dirname, rootDir);
  let filenames = klawSync(absRootDir, { nodir: true })
    .map(file => file.path)
    .map(file => file.replace(absRootDir, ''))
    .map(file => file.replace(/\\/g, '/'))
    .map(file => '<rootDir>' + file);
  filenames = mm(filenames, testMatch);
  testPathIgnorePatterns = mm.not(filenames, sequentialTestPathMatchPatterns);
}

module.exports = {
  rootDir,
  setupFiles: [
    '../setup.js',
  ],
  testMatch,
  testPathIgnorePatterns,
};

The updated jest.config.js depends on jest-config, klaw-sync, and micromatch.

npm install --save-dev jest-config klaw-sync micromatch

Now, you can run npm run test:integration:sequential if you only want to run the tests that need to be run sequentially.

Or run npm run test:integration:parallel for the parallel tests.

Or run npm run test:integration to first run the sequential tests. Then when that is finished, the parallel tests will run.

Or run npm run test to run both the unit and integration tests.

Note: The directory structure I am using with my unit and integration tests is as follows:

__tests__
  integration
    src
      *.spec.js
      *.test.js
    jest.config.js
  unit
    src
      *.spec.js
      *.test.js
    jest.config.js