runtime/trace: TestSubscribers failures

[gopherbot]

#!watchflakes
default <- pkg == "runtime/trace" && test ~ `TestSubscribers`

Issue created automatically to collect these failures.

Example (log):

=== RUN   TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight)
    subscribe_test.go:41: unexpected error reading trace for flightRecorder: expected a goroutine but didn't have one
--- FAIL: TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight) (0.01s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "runtime/trace" && test == "TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight)"

2025-09-29 21:06 gotip-netbsd-arm64 go@fc88e18b runtime/trace.TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight) (log)

=== RUN   TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight)
    subscribe_test.go:41: unexpected error reading trace for flightRecorder: expected a goroutine but didn't have one
--- FAIL: TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight) (0.01s)

— watchflakes

[mknyszek]

Let's wait for another failure, but in the meantime we should change the test to dump the trace.

[gopherbot]

Change https://go.dev/cl/710755 mentions this issue: runtime/trace: dump test traces on validation failure

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "runtime/trace" && test == "TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight)"

2025-11-20 23:01 gotip-linux-amd64_avx512 go@d58b7336 runtime/trace.TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight) (log)

=== RUN   TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight)
    subscribe_test.go:41: unexpected error reading trace for flightRecorder: expected a goroutine but didn't have one
--- FAIL: TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight) (0.00s)

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "runtime/trace" && test == "TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight)"

2025-11-21 20:42 gotip-netbsd-arm64 go@e15800c0 runtime/trace.TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight) (log)

=== RUN   TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight)
    subscribe_test.go:41: unexpected error reading trace for flightRecorder: expected a goroutine but didn't have one
--- FAIL: TestSubscribers/start(trace)_start(flight)_stop(trace)_stop(flight) (0.01s)

— watchflakes