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

Another possibility is that ts-jest is slow. There was an issue about that, and it was not completely resolved.

There are various workarounds discussed. They consist of setting isolatedModules=true and also --maxWorkers=1. That is, in jest.config.js

'use strict';  module.exports = {     preset: 'ts-jest',     testEnvironment: 'node',     globals: {         'ts-jest': {             isolatedModules: true         }     }, } 

and run

yarn test --maxWorkers=1 

Could be worth trying. Alternatively, it is possible to forgo ts-jest and use babel transpilation.

Answer 2

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.