1 files changed, 62 insertions, 0 deletions
diff --git a/src/cmd/trace/trace_test.go b/src/cmd/trace/trace_test.go
new file mode 100644
index 0000000000..73a2883f1e
--- /dev/null
+++ b/src/cmd/trace/trace_test.go
@@ -0,0 +1,62 @@
+package main
+
+import (
+	"internal/trace"
+	"testing"
+)
+
+// TestGoroutineCount tests runnable/running goroutine counts computed by generateTrace
+// remain in the valid range.
+//   - the counts must not be negative. generateTrace will return an error.
+//   - the counts must not include goroutines blocked waiting on channels or in syscall.
+func TestGoroutineCount(t *testing.T) {
+	w := trace.NewWriter()
+	w.Emit(trace.EvBatch, 0, 0)  // start of per-P batch event [pid, timestamp]
+	w.Emit(trace.EvFrequency, 1) // [ticks per second]
+
+	// In this test, we assume a valid trace contains EvGoWaiting or EvGoInSyscall
+	// event for every blocked goroutine.
+
+	// goroutine 10: blocked
+	w.Emit(trace.EvGoCreate, 1, 10, 1, 1) // [timestamp, new goroutine id, new stack id, stack id]
+	w.Emit(trace.EvGoWaiting, 1, 10)      // [timestamp, goroutine id]
+
+	// goroutine 20: in syscall
+	w.Emit(trace.EvGoCreate, 1, 20, 2, 1)
+	w.Emit(trace.EvGoInSyscall, 1, 20) // [timestamp, goroutine id]
+
+	// goroutine 30: runnable
+	w.Emit(trace.EvGoCreate, 1, 30, 5, 1)
+
+	w.Emit(trace.EvProcStart, 2, 0) // [timestamp, thread id]
+
+	// goroutine 40: runnable->running->runnable
+	w.Emit(trace.EvGoCreate, 1, 40, 7, 1)
+	w.Emit(trace.EvGoStartLocal, 1, 40) // [timestamp, goroutine id]
+	w.Emit(trace.EvGoSched, 1, 8)       // [timestamp, stack]
+
+	events, err := trace.Parse(w, "")
+	if err != nil {
+		t.Fatalf("failed to parse test trace: %v", err)
+	}
+
+	params := &traceParams{
+		events:  events,
+		endTime: int64(1<<63 - 1),
+	}
+
+	// If the counts drop below 0, generateTrace will return an error.
+	viewerData, err := generateTrace(params)
+	if err != nil {
+		t.Fatalf("generateTrace failed: %v", err)
+	}
+	for _, ev := range viewerData.Events {
+		if ev.Name == "Goroutines" {
+			cnt := ev.Arg.(*goroutineCountersArg)
+			if cnt.Runnable+cnt.Running > 2 {
+				t.Errorf("goroutine count=%+v; want no more than 2 goroutines in runnable/running state", cnt)
+			}
+			t.Logf("read %+v %+v", ev, cnt)
+		}
+	}
+}