After upgrade to CRA 2.0, tests run very slow.

[ektomorfik]

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.)

[Timer]

Did you use the Node test environment previously? We switched the default to JSDOM which has some overhead.

[ektomorfik]

I used default settings

[ektomorfik]

Maybe it would help a bit. Some time ago, I setup next.js project with Jest 23 and I had the same issue. I solved problem by downgrade Jest to 22.x.x.

[gaearon]

cc @rogeliog is there a reason to expect slowdown in 23?

[rogeliog]

I don’t think so, any ideas @SimenB @thymikee?

[SimenB]

We've had reports of slowdown on windows, see e.g. jestjs/jest#6783

We haven't been able to pin it down, though, unfortunately...

[thymikee]

IIRC this was slowing down watch mode a bit: jestjs/jest#6647

[rogeliog]

@SimenB do you know if the issue is only affecting windows?
@ektomorfik do they also run slower when you run them in "non watch mode"(i.e CI=true npm run test)

[bugzpodder]

I've had cases where I saw a big slow down on mac and not on watch mode. Two snapshot tests took over 30 seconds to run (and time varies on different runs). Will test it a bit more today and see if i can file something.

[rogeliog]

I set up a repo locally where I run 100 test suites to benchmark jest@21, jest@22 and jest@23. It seems that... All tests suites have this exact code.

describe('Simple assertions', () => {
  it('has a simple assertion', () => {
    expect(1).toBe(1);
  });

  it('using matchers', () => {
    expect({
      username: 'foo',
      password: '123456'
    }).toMatchObject(expect.objectContaining({
      username: 'foo'
    }));
  });
})

And I am running them all in non-watch mode. Jest@23 is running slower in my benchmark. After doing a lot of git bisect and I see a big performance hit introduced in this PR jestjs/jest#5932... Checking out a version right before that PR performs way better, any thoughts @cpojer?

[SimenB]

Hmmm, might be related to jestjs/jest#6694

Maybe we should look into caching module lookups?