The coverage utils depend on `src/api.ts` being up to date and pointing to the right modules. If they aren't, you would get a cryptic error on CI:
```
1) "before all" hook in "{root}":
TypeError: Cannot read property 'prototype' of undefined
at traceAPICoverage (test/coverage-utils.js:40:54)
at Context.before (test/coverage-utils.js:103:7)
2) "after all" hook in "{root}":
TypeError: Cannot read property 'stop' of undefined
at Context.after (test/mocha-utils.js:168:22)
```
This change logs a clearer error that highlights the missing class and exits, so it's much easier to realise what's gone wrong.
Ideally the coverage wouldn't need a hardcoded list of sources, but until then this will help spot this error in the future.
* chore: update how we track coverage during unit tests
The old method of tracking coverage was causing issues. If a test failed
on CI, that test's failure would be lost because the test failing would
in turn cause the coverage to fail, but the `process.exit(1)` in the
coverage code caused Mocha to not output anything useful.
Instead the coverage checker now:
* tracks the coverage in memory in a Map (this hasn't changed)
* after all tests, writes that to disk in test/coverage.json (which is
gitignored)
* we then run a single Mocha test that asserts every method was called.
This means if the test run fails, the build will fail and give the error
about that test run, and that output won't be lost when the coverage
then fails too.
Co-authored-by: Mathias Bynens <mathias@qiwi.be>
Rather than maintain our own test runner we should instead lean on the community and use Mocha which is very popular and also our test runner of choice in DevTools too.
Note that this commit doesn't remove the TestRunner source as it's still used for other unit tests, but they will be updated in a future PR and then we can remove the TestRunner.
The main bulk of this PR is updating the tests as the old TestRunner passed in contextual data via the `it` function callback whereas Mocha does not, so we introduce some helpers for the tests to make it easier.
