It fails because the config is now passed to Jest explicitly.
But the test doesn't know about the config.

To fix this, we just run it via `yarn test` (which includes the config).
We already depend on Yarn for development anyway.

This produces a bunch of errors:

Test Suites: 64 failed, 58 passed, 122 total
Tests:       740 failed, 26 skipped, 1809 passed, 2575 total
Snapshots:   16 failed, 4 passed, 20 total

Down from 740 to 175 failed.

Test Suites: 44 failed, 78 passed, 122 total
Tests:       175 failed, 26 skipped, 2374 passed, 2575 total
Snapshots:   16 failed, 4 passed, 20 total

Down from 175 to 129.

Test Suites: 33 failed, 89 passed, 122 total
Tests:       129 failed, 1029 skipped, 1417 passed, 2575 total
Snapshots:   16 failed, 4 passed, 20 total

There is no need for it now. The only test that was special is moved into ReactDOM-test.

The tests now run in production in a separate pass.

This ensures that by default we expect no warnings in production bundles.
If the warning *is* expected, use the regular spyOn() method.

This currently breaks all expectDev() assertions without __DEV__ blocks so we go back to:

Test Suites: 56 failed, 65 passed, 121 total
Tests:       379 failed, 1029 skipped, 1148 passed, 2556 total
Snapshots:   16 failed, 4 passed, 20 total

We started using spyOnDev() for console warnings to ensure we don't *expect* them to occur in production. As a consequence, expectDev() assertions on console.error.calls fail because console.error.calls doesn't exist. This is actually good because it would help catch accidental warnings in production.

To solve this, we are getting rid of expectDev() altogether, and instead introduce explicit expectation branches. We'd need them anyway for testing intentional behavior differences.

This commit replaces all expectDev() calls with expect() calls in __DEV__ blocks. It also removes a few unnecessary expect() checks that no warnings were produced (by also removing the corresponding spyOnDev() calls).

Some DEV-only assertions used plain expect(). Those were also moved into __DEV__ blocks.

ReactFiberErrorLogger was special because it console.error()'s in production too. So in that case I intentionally used spyOn() instead of spyOnDev(), and added extra assertions.

This gets us down to:

Test Suites: 21 failed, 100 passed, 121 total
Tests:       72 failed, 26 skipped, 2458 passed, 2556 total
Snapshots:   16 failed, 4 passed, 20 total

We could've disabled it, but seems like a good idea to test since we use it at FB.

This is one of the few places where DEV and PROD behavior differs for performance reasons.
Now we explicitly test both branches.

This logic is really complicated because of the global ReactFiberErrorLogger mock.
I understand it now, so I added TODOs for later.

It can be much simpler if we change the rest of the tests that assert uncaught errors to also assert they are logged as warnings.
Which mirrors what happens in practice anyway.

It is very likely unintentional but I don't want to change behavior in this PR.
Filed a follow up as facebook#11618.

We used to before, too. I just forgot to add the arguments after deleting the script.