testing: diagnose a potential misuse of RunParallel

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/68030043

diff --git a/src/pkg/testing/benchmark.go b/src/pkg/testing/benchmark.go
index e6f3c6d7903214c776d08afa983a56b7252e520d..06b5b603e3948bedce1f9f7db1f72ad84d84a9fb 100644 (file)
--- a/src/pkg/testing/benchmark.go
+++ b/src/pkg/testing/benchmark.go
@@ -417,6 +417,9 @@ func (b *B) RunParallel(body func(*PB)) {
                }()
        }
        wg.Wait()
+       if n == 0 {
+               b.Fatal("RunParallel body did not not call PB.Next")
+       }
 }
 
 // SetParallelism sets the number of goroutines used by RunParallel to p*GOMAXPROCS.