stress: skip.UnderStress() doesn't

[HonoreDB]

Describe the problem

skip.UnderStress(), skip.UnderStressRace(), and skip.NightlyStress() all reference the COCKROACH_NIGHTLY_STRESS environment variable to check if we're running under stress. This variable isn't set by make stress or ./dev test --stress, though, it's set by shell scripts that call those commands. So running dev test --stress locally won't skip those tests.

I haven't done the forensics to figure out whether this is intentional--it's plausibly a good idea. But it is definitely confusing, because some people will use skip.UnderStress if they have a test that fails under stress (due to a timeout or something) and thus effectively break ./dev test --stress for their package outside nightly test runs.

To Reproduce

Create a test that goes

skip.UnderStress(t)
t.FailNow()

and run it with ./dev test --stress.

Expected behavior

Maybe rename it to skip.UnderNightlyStress() and call it a day?

My preference though would I think be to have the ability to actually skip tests under stress. For example, right after I file this issue I'm going to go add skip.UnderStressRace() to TestChangefeedRestartMultiNode because it reliably hangs under stressrace, I think because it's calling TestCluster.WaitForFullReplication() and under stressrace we just never get there. I'd rather not have that be a trap for anyone running tests locally.

So maybe --stress could set a different flag that's also visible to skip, and then we could have an API like

skip.WhenExpensive() // skips when SKIP_EXPENSIVE_TESTS is set, set this in nightly stress tests
skip.UnderStress() // skips when CRDB_STRESS is set, set this during all stress invocations

Jira issue: CRDB-17584