This patch migrates tests so that they can be run concurrently.
- By default, tests still run in one thread.
- To run tests in 4 parallel threads, run node test/test.js -j 4 or npm run unit -- -j 4
- Environment variable PPTR_PARALLEL_TESTS could be set to override default parallelization
Every test gets passed in a state. State is set up in the beforeAll and beforeEach callbacks,
and should be teared down in the afterAll and afterEach callbacks.
By default, state has a parallelIndex variable initialized that defines the thread index that runs the execution.
This patch introduces a tiny test runner to run puppeteer tests.
The test runner is self-container and allows parallel (wrt IO) test execution.
It will also allow us to split tests into multiple files if necessary.
Comparing to the jasmine, the testrunner supports parallel execution, properly
handles "unhandled promise rejection" event and signals.
Comparing to ava/jest, the testrunner doesn't run multiple node processes,
which makes it simpler but sufficient for our goals.
