Migration of tests to Jest

[niieani]

@ooflorent Alright, I've done it.

This is with jest:

Test Suites: 1 failed, 65 passed, 66 total
Tests:       1 failed, 126 skipped, 10692 passed, 10819 total
Snapshots:   2 passed, 2 total
Time:        141.898s, estimated 158s
Ran all test suites.

This was before on the same computer with mocha:

  10713 passing (13m)
  127 pending

That's an improvement of almost 6x in terms of speed.

(fewer total number of tests under Mocha, cause I run that test around 4.0-alpha, before merging current master)

```
 FAIL  test/TestCasesDevelopment.test.js (13.204s)
  ● TestCases › development › chunks › runtime › exported tests › should not load a chunk which is included in a already loaded one

    expect(received).toBe(expected) // Object.is equality

    Expected: true
    Received: false

      175 |             __webpack_require__.e(/*! require.ensure */3).then((function(require) {
      176 |                     try {
    > 177 |                             expect(sync).toBe(true);
      178 |                             done();
      179 |                     } catch(e) {
      180 |                             done(e);

      at test/js/development/chunks/runtime/bundle.js:177:18
```

~~~We still need facebook/jest#5673 to ship before we can merge, but this is ready for review.~~~

[sokra]

Looks good, I noticed one small issue. When running jest in watch mode and running the WatchDetection test, sane emits EPERM errors on windows. sane doesn't seem to check the ignore list when directories are added (/~https://github.com/amasad/sane/blob/master/src/node_watcher.js#L310) and reading the stats from a removed file seem to cause an EPERM error here (/~https://github.com/amasad/sane/blob/master/src/node_watcher.js#L306). I believe it's an sane issue. Although it would also be great if watcher errors would be catched (via watcher.on("error")) in jest-haste-map. Anyway, it's not super critical.

[webpack-bot]

@sokra Thanks for your update.

I labeled the Pull Request so reviewers will review it again.

@shellscape Please review the new changes.

[sokra]

Awesome thanks

[devenbansod]

Awesome stuff @niieani !

Thanks @skovhus for /~https://github.com/skovhus/jest-codemods 🙌

Just throwing it out there:
I had faced some similar issues while transforming test assertions for babel's tests, which had a mix of mocha, chai, assert in babel/babel#7476. I feel I should have noted these down, and regret not reporting them to /~https://github.com/skovhus/jest-codemods then.

But then I wrote a (seriously) toned down version focusing on assertions that babel's tests required at: /~https://github.com/devenbansod/jest-expect-codemod

[sokra]

I got this random error in watch mode after changing a file. Can't reproduce...

D:\Repos\webpack\node_modules\jest-runtime\build\index.js:581
    const wrapper = this._environment.runScript(transformedFile.script)[
                                                                       ^

TypeError: Cannot read property 'Object.<anonymous>' of null
    at Runtime._execModule (D:\Repos\webpack\node_modules\jest-runtime\build\index.js:581:72)
    at Runtime.requireModule (D:\Repos\webpack\node_modules\jest-runtime\build\index.js:365:14)
    at Runtime.requireModuleOrMock (D:\Repos\webpack\node_modules\jest-runtime\build\index.js:449:19)
    at readdir (D:\Repos\webpack\node_modules\readdirp\readdirp.js:55:25)
    at FSWatcher.<anonymous> (D:\Repos\webpack\node_modules\chokidar\lib\nodefs-handler.js:356:5)
    at FSWatcher.Object.<anonymous>.NodeFsHandler._handleDir (D:\Repos\webpack\node_modules\chokidar\lib\nodefs-handler.js:407:18)
    at FSWatcher.<anonymous> (D:\Repos\webpack\node_modules\chokidar\lib\nodefs-handler.js:456:19)
    at FSWatcher.<anonymous> (D:\Repos\webpack\node_modules\chokidar\lib\nodefs-handler.js:461:16)
    at D:\Repos\webpack\node_modules\graceful-fs\polyfills.js:287:18
    at FSReqWrap.oncomplete (fs.js:153:5)

[sokra]

@niieani What's the reason for using Math.random().toPrecision(21).slice(2) in the folder name for watch-src tests?

[sokra]

I also ran into this issue jestjs/jest#4820 but no blocker

[sokra]

The slashes are also a bit weird here, but not important (windows)

[sokra]

When running jest in watch mode and running the WatchDetection test, sane emits EPERM errors on windows. sane doesn't seem to check the ignore list when directories are added (/~https://github.com/amasad/sane/blob/master/src/node_watcher.js#L310) and reading the stats from a removed file seem to cause an EPERM error here (/~https://github.com/amasad/sane/blob/master/src/node_watcher.js#L306). I believe it's an sane issue. Although it would also be great if watcher errors would be catched (via watcher.on("error")) in jest-haste-map. Anyway, it's not super critical.

It's worse than I original estimated. The whole jest watch process crashes.

Please handle the error event in jest-haste-map.

[niieani]

@sokra Math.random().toPrecision(21).slice(2) is needed to always create a new folder. Jest creates their haste map, I think based on package.json files. When there are duplicates of the same path and the same package name, it can cause issues.

Not sure what to do with the Windows issues, I'm on macOS. :/