tests(unit): retry failures and upload failure artifacts

[adamraine]

Unit failures are only happening in CI, failure artifacts might give us more insight. Retry unit tests 5 times to unblock CI.

CI failures added to backlog: #15382

[connorjclark]

oh. we need to support this in the script. can you not remove ?

[adamraine]

The --forbid-only flag doesn't work when we use it like this. This PR adds it to run-mocha-tests.js and gives it a default value of true in CI instead.

[connorjclark]

What do you mean it doesn't work when used like this?

I know it doesn't work at all w/o this PR or #15383 , but I don't understand your meaning here

[adamraine]

Two reasons:

• Before this PR we didn't pipe the --forbid-only option into mocha
• We would need to do npm run unit -- --forbid-ony to pass the flag all the way down

Instead of messing with the flags in the package scripts, I would prefer to just look at process.env.CI. We already do this for --parallel in run-mocha-tests.js:

lighthouse/core/test/scripts/run-mocha-tests.js

Lines 127 to 132 in 06ebc36

	// Although much faster, mocha's parallel test runner defers printing errors until
	// all tests have finished. This may be undesired for local development, so enable
	// parallel mode by default only in CI.
	// Also, good to default to false locally because that avoids missing cross-file
	// test contamination by chance of mocha splitting up the work in a way that hides it.
	default: Boolean(process.env.CI),