jobs: TestJitterCalculation failed

[cockroach-teamcity]

jobs.TestJitterCalculation failed with artifacts on master @ 9915bd965cab50ff5e7c9214447a360deec67cd5:

=== RUN   TestJitterCalculation
--- FAIL: TestJitterCalculation (0.00s)
=== RUN   TestJitterCalculation/small
    registry_test.go:1236: 
        	Error Trace:	github.com/cockroachdb/cockroach/pkg/jobs/registry_test.go:1236
        	Error:      	Should not be: 1000000
        	Test:       	TestJitterCalculation/small
    --- FAIL: TestJitterCalculation/small (0.00s)

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See also: How To Investigate a Go Test Failure (internal)

/cc @cockroachdb/jobs @cockroachdb/disaster-recovery

This test on roachdash | Improve this report!

Jira issue: CRDB-40985

[msbutler]

This failed because the jitter function didn't move the input value. This can happen very rarely if rand.Float64 returns something that rounds to 0.5:

func jitter(dur time.Duration) time.Duration {
	const jitter = 1.0 / 6.0
	jitterFraction := 1 + (2*rand.Float64()-1)*jitter // 1 + [-1/6, +1/6)
	return time.Duration(float64(dur) * jitterFraction)
}

[msbutler]

The probability of this occurring is tiny. I'm going to close this out. If it happens again, we could add a retry loop to this test.