testing: detect early return from B.Loop
Currently, if a benchmark function returns prior to B.Loop() returning
false, we'll report a bogus result. While there was no way to detect
this with b.N-style benchmarks, one way b.Loop()-style benchmarks are
more robust is that we *can* detect it.
This CL adds a flag to B that tracks if B.Loop() has finished and
checks it after the benchmark completes. If there was an early exit
(not caused by another error), it reports a B.Error.
Fixes #72933.
Updates #72971.
Change-Id: I731c1350e6df938c0ffa08fcedc11dc147e78854
Reviewed-on: https://go-review.googlesource.com/c/go/+/659656
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Austin Clements <austin@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>