Jest - Simple tests are slow

Question

I am using Jest to test an angular app and it is taking a really long time for simple tests to run and I can not seem to figure out why.

My Jest setup in package.json:

"jest": {
  "modulePaths": [
    "<rootDir>/src",
    "<rootDir>/node_modules"
  ],
  "testPathIgnorePatterns": [
    ".git/.*",
    "node_modules/.*"
  ],
  "transformIgnorePatterns": [
    "node_modules/.*",
    ".*\\.js"
  ],
  "setupTestFrameworkScriptFile": "<rootDir>/src/setupJest.js",
  "preset": "jest-preset-angular",
  "testEnvironment": "jsdom",
  "testRegex": "src/app/.*\\.spec\\.ts$",
  "moduleFileExtensions": [
    "ts",
    "js",
    "json"
  ],
  "verbose": true,
  "cacheDirectory": ".jest-cache",
  "coveragePathIgnorePatterns": [
    ".*\\.(shim\\.ngstyle|ngfactory)\\.ts"
  ],
  "globals": {
    "ts-jest": {
      "tsConfigFile": "./tsconfig.json"
    },
    "__TRANSFORM_HTML__": true
  }
}

My Jest setup file:

'use strict';
require('core-js/es6/reflect');
require('core-js/es7/reflect');
require('zone.js');
require('zone.js/dist/proxy.js');
require('zone.js/dist/sync-test');
require('zone.js/dist/async-test');
require('zone.js/dist/fake-async-test');
require('jest-zone-patch');

const getTestBed = require('@angular/core/testing').getTestBed;
const BrowserDynamicTestingModule = require('@angular/platform-browser-dynamic/testing').BrowserDynamicTestingModule;
const platformBrowserDynamicTesting = require('@angular/platform-browser-dynamic/testing')  .platformBrowserDynamicTesting;

getTestBed().initTestEnvironment(
    BrowserDynamicTestingModule,
    platformBrowserDynamicTesting()
);

Here is my simple test:

fdescribe('RichTextEditorComponent', () => {
  it('should be fast', () => {
    expect(true).toBeTruthy();
  });
});

Does anyone have any idea as to why this is taking 9+ seconds?

Answer 1

Read these two links:

https://itnext.io/how-to-make-your-sluggish-jest-v23-tests-go-faster-1d4f3388bcdd https://github.com/facebook/jest/issues/7963

Here's a list of things to consider. They aren't specific to your case, but since the title of the question is quite general I thought they might help some percentage of visitors. They shouldn't be tried blindly, they are simply a starting point to research.

Things to try to speed up your jest tests:

1. Run in watch mode with --watch

   jest optimizes when you use --watch.

2. run on your host computer instead of in docker? -> I was previously using docker exec -it <containername> yarn test and found it faster when I changed to using my host.

3. upgrade jest version it seems like there were some bugs that made some versions slower https://github.com/facebook/jest/pull/8046

   note: that yarn upgrade obeys the ~ and ^ version signifiers, if you know what you're doing, you might just want to remove and re add yarn remove jest yarn add -D jest that will just get you the latest

4. change the test environment from jsdom to node

"jest": {
  "testEnvironment": "node"
}

5. Run the tests syncronously.. allows jest to optimize?

add --runInBand option

6. Setting max workers might make it faster?

add --maxWorkers=4 option

In my case I upgraded the jest version, started using --watch and --runInBand and running on my host instead of via docker, and my test time went from 2 mins to 10 seconds. I don't know what the problem was exactly in my case.