This ensures we get a proper error when something goes wrong. Should
also help with producing the right error code in the case of internal error.
Drive-by: fix location issue which manifests on the bots.
Drive-by: remove the use of Array.prototype.flat to make it work on bots.
This patch re-implements matching and reporting for test runner.
Among other improvements:
- test failures now show a short snippet from test
- test failures now explicitly say what received and what was expected
- `expect.toBe()` now does text diff when gets strings as input
- `expect.toEqual` now does object diff
