.

go/internal/xtracing/tracetest/example_test.go

@@ -18,6 +18,8 @@
 // See https://www.nexedi.com/licensing for rationale and options.
 
 // Package tracetest_test demonstrates how to use package tracetest.
+//
+// It also serves as set of testcases for tracetest itself.
 package tracetest_test
 
 //go:generate gotrace gen .
@@ -36,26 +38,20 @@ import (
 
 //trace:event traceHi(who string)
 //trace:event traceHello(who string)
-
 func hi(who string) {
 	traceHi(who)
 	fmt.Println("Hi,", who)
 }
-
 func hello(who string) {
 	traceHello(who)
 	fmt.Println("Hello,", who)
 }
 
-// TestExample demonstrates how to use tracetest to verify concurrent system with 2 threads.
-func TestExample(t *testing.T) {
-	tracetest.Verify(t, tracetestExample)
-}
-func tracetestExample(t *tracetest.T) {
-	type eventHi string
-	type eventHello string
-
-	// setup tracing to deliver trace events to t.
+// we use tracing to attach probes to hi and hello, and emit corresponding
+// eventHi and eventHello to tracetest.T from there.
+type eventHi string
+type eventHello string
+func setupTracing(t *tracetest.T) *tracing.ProbeGroup {
 	pg := &tracing.ProbeGroup{}
 	tracing.Lock()
 	traceHi_Attach(pg, func(who string) {
@@ -65,30 +61,43 @@ func tracetestExample(t *tracetest.T) {
 		t.RxEvent(eventHello(who))
 	})
 	tracing.Unlock()
+	return pg
+}
+
+// routeEvent tells to which stream an event should go.
+// Here, in example, we use the convention that who comes as "<threadID>·..."
+// and we route the event to stream that corresponds to threadID.
+func routeEvent(event interface{}) (stream string) {
+	who := ""
+	switch ev := event.(type) {
+	default:
+		panic(fmt.Sprintf("unexpected event type %T", event))
+	case eventHi:
+		who = string(ev)
+	case eventHello:
+		who = string(ev)
+	}
+
+	i := strings.Index(who, "·")
+	if i == -1 {
+		panic(fmt.Sprintf("who does not have threadID: %q", who))
+	}
+
+	return strings.ToLower(who[:i])
+}
+
+
+// TestExample demonstrates how to use tracetest to verify concurrent system with 2 threads.
+func TestExample(t *testing.T) {
+	tracetest.Verify(t, tracetestExample)
+}
+func tracetestExample(t *tracetest.T) {
+	// setup tracing to deliver trace events to t.
+	pg := setupTracing(t)
 	defer pg.Done()
 
 	// tell tracetest to which stream an event should go.
-	t.SetEventRouter(func(event interface{}) (stream string) {
-		// it can be only eventHi and eventHello.
-		// in this test the convention is that who comes as <threadID>·...
-		// we used threadID as stream.
-		who := ""
-		switch ev := event.(type) {
-		default:
-			panic(fmt.Sprintf("unexpected event type %T", event))
-		case eventHi:
-			who = string(ev)
-		case eventHello:
-			who = string(ev)
-		}
-
-		i := strings.Index(who, "·")
-		if i == -1 {
-			panic(fmt.Sprintf("who does not have threadID: %q", who))
-		}
-
-		return strings.ToLower(who[:i])
-	})
+	t.SetEventRouter(routeEvent)
 
 	// run the workload
 	var wg sync.WaitGroup