Testing library to remove dependency on mocha

[lewish]

Mocha causes us a few issues, as it needs to be run through the CLI, we have complex bazel rules to deal with this. It has annoyingly globally scoped types and does a lot more than we need it to.

This PR introduces a simple testing library that can be used without a CLI, where each test is simply considered a binary with a exit set according to whether it passes or not. It also adds rules ts_test and ts_test_suite for making writing bazel rules easier.

The library itself is otherwise very similar to mocha, without the globals, CLI, and slightly more strict usage patterns.

Features:

• Parallel test suites
• Timeouts
• Sub suites
• Hooks: beforeEach, afterEach, setUp, tearDown
• Deep diffing on log output
• Log format that matches bazel

In the future, we should I think be able to use bazel for coverage metrics without any additional effort with this set up after this work is finished: bazel-contrib/rules_nodejs#1135

[BenBirt]

1. do we need to add some code here to pay attention to bazel timeout rules?
2. is any of this output conforming to some bazel format, or no? if so, can you document it?

[lewish]

Types for test/suite etc are clearer to read for consumers now:

Bazel timeout - not clear what we can do here? Bazel hard times out tests after something like 5 mins.

R.e. output, it's bazel-esque, unfortunately I can't get the colors working properly, but it used the same colors for PASSED, FAILED etc:

suite > fails on promise rejection                                       FAILED

    Error: fail-async
        at testing/index.spec.ts:28:30
        at Generator.next (<anonymous>)
        at /home/lewis/.cache/bazel/_bazel_lewis/34cd37228b66f7a6f769c3c562621852/sandbox/linux-sandbox/19/execroot/df/bazel-out/k8-py2-fastbuild/bin/testing/index.spec.sh.runfiles/df/testing/index.spec.js:6:71
        at new Promise (<anonymous>)
        at __awaiter (/home/lewis/.cache/bazel/_bazel_lewis/34cd37228b66f7a6f769c3c562621852/sandbox/linux-sandbox/19/execroot/df/bazel-out/k8-py2-fastbuild/bin/testing/index.spec.sh.runfiles/df/testing/index.spec.js:2:12)
        at Test.fn (testing/index.spec.ts:27:53)
        at Test.<anonymous> (testing/test.ts:51:14)
        at Generator.next (<anonymous>)
        at /home/lewis/.cache/bazel/_bazel_lewis/34cd37228b66f7a6f769c3c562621852/sandbox/linux-sandbox/19/execroot/df/bazel-out/k8-py2-fastbuild/bin/testing/index.spec.sh.runfiles/df/testing/test.js:6:71
        at new Promise (<anonymous>)

suite > times out                                                       TIMEOUT

    Error: Timed out (10ms).
        at Timeout.<anonymous> (testing/test.ts:55:20)
        at listOnTimeout (internal/timers.js:531:17)
        at processTimers (internal/timers.js:475:7)


Tests failed.
================================================================================
INFO: Elapsed time: 1.064s, Critical Path: 0.80s
INFO: 4 processes: 2 linux-sandbox, 2 worker.
INFO: Build completed successfully, 5 total actions
//testing:index.spec                                                     PASSED in 0.2s

[BenBirt]

timeouts - i only took a quick scan, but IMO your runner should be obeying the various parameters in https://docs.bazel.build/versions/master/test-encyclopedia.html, including timeouts.

[lewish]

timeouts - i only took a quick scan, but IMO your runner should be obeying the various parameters in https://docs.bazel.build/versions/master/test-encyclopedia.html, including timeouts.

As discussed, reading that page I don't think the test code is supposed to do anything with these flags. Bazel will kill processes and tests if they time out itself.

[lewish]

As discussed, re-allowing calling of top level suite/test methods inside tests, as this was IMO more annoying than it was worth after trying to migrate tests.