After upgrade to CRA 2.0, tests run very slow.

Is this a bug report?

I think so.

After upgrade to CRA 2.0 Jest tests run much slower than before. I think it could be made by Jest 23

Did you try recovering your dependencies?

yes, but problem still exists

Which terms did you search for in User Guide?

Running Tests

Environment

Environment: OS: Windows 10 Node: 8.11.2 Yarn: 1.10.1 npm: 6.4.1 Watchman: Not Found Xcode: N/A Android Studio: Not Found

Packages: (wanted => installed) react: ^16.5.2 => 16.5.2 react-dom: ^16.5.2 => 16.5.2 react-scripts: 2.0.3 => 2.0.3

Steps to Reproduce

Tests in previous version reloaded less than 1s. After upgrade to CRA 2.0 tests reload in about 3-4sec. Problec occurs even if I create new empty project

1. create-react-app app
2. npm run test

Expected Behavior

It should be faster 😦

Actual Behavior

Reproducible Demo

(Paste the link to an example project and exact instructions to reproduce the issue.)

[empz]

Fresh create-react-app (2.1.1).

 PASS  src/App.test.js
  √ renders without crashing (41ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        6.447s
Ran all test suites.

Watch Usage: Press w to show more.

So while the test actually seems to run pretty fast (41ms), the setup takes 6 seconds. Re-running doesn’t make it faster.

Windows 10 x64, I7 4690K, SSD…

[lukaszczernal]

We also struggle with slow tests if we run: react-scripts-ts test --env=jsdom

but if we run them with coverage flag they are way faster react-scripts-ts test --env=jsdom --coverage

I understand that it should be the opposite 😃

We are running: "react": "^16.2.0", "react-dom": "^16.2.0", "react-redux": "^5.0.6", "react-router-dom": "^4.2.2", "react-scripts-ts": "2.17.0", "enzyme-adapter-react-16": "^1.1.1",