fix: only show runparalllel warning once to avoid spamming the console

Author: not-matthias

testing/testing/benchmark.go

@@ -39,6 +39,8 @@ var (
 	benchmarkMemory *bool
 
 	benchTime = durationOrCountFlag{d: 1 * time.Second} // changed during test of testing package
+
+	runParallelWarningOnce sync.Once
 )
 
 type durationOrCountFlag struct {
@@ -1177,11 +1179,12 @@ func (pb *PB) Next() bool {
 // RunParallel reports ns/op values as wall time for the benchmark as a whole,
 // not the sum of wall time or CPU time over each parallel goroutine.
 func (b *B) RunParallel(body func(*PB)) {
-	fmt.Println("RunParallel is currently unsupported when running with CodSpeed. Continuing without measurements...")
-
 	if b.N == 0 {
 		return // Nothing to do when probing.
 	}
+	runParallelWarningOnce.Do(func() {
+		fmt.Println("WARNING: RunParallel is currently unsupported when running with CodSpeed. Continuing without measurements...")
+	})
 	// Calculate grain size as number of iterations that take ~100µs.
 	// 100µs is enough to amortize the overhead and provide sufficient
 	// dynamic load balancing.