This change introduces a TestWorker that can be in a certain state,
meaning it has run some beforeAll hooks of a certain test suite stack.
TestWorker can be created at any time, which allows for a number of features:
- don't run hooks for suites with no runnable tests;
- smarter test distribution (and possibility for variuos strategies);
- recovering from hook failures and test failure by creating a new worker;
- possible isolation between workers by running them in separate environments.
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
