fix galley fssource flakey test (istio#9524)

* fix galley fssource flakey test

* fix galley fssource flakey test

* fix mixer lint issue

galley/pkg/fs/fssource_test.go

@@ -21,6 +21,7 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	"istio.io/istio/galley/pkg/runtime/resource"
 )
@@ -326,16 +327,16 @@ func TestFsSource_DeletePartResorceInFile(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Unexpected error: %v", err)
 	}
-
-	log := logChannelOutput(ch, 4)
+	donec := make(chan bool)
 	expected := "[Event](Deleted: [VKey](type.googleapis.com/istio.policy.v1beta1.Rule:some.mixer.rule @v0))"
-
-	if log != expected {
-		t.Fatalf("Event mismatch:\nActual:\n%s\nExpected:\n%s\n", log, expected)
+	go checkEventOccurs(expected, ch, donec)
+	select {
+	case <-time.After(5 * time.Second):
+		t.Fatalf("Expected Event does not occur:\n%s\n", expected)
+	case <-donec:
+		return
 	}
-
 	s.Stop()
-
 }
 
 //Only log the last event out
@@ -346,3 +347,12 @@ func logChannelOutput(ch chan resource.Event, count int) string {
 	}
 	return strings.TrimSpace(fmt.Sprintf("%v\n", result))
 }
+
+// Check whether a specif event occurs
+func checkEventOccurs(expectedEvent string, ch chan resource.Event, donec chan bool) {
+	for event := range ch {
+		if expectedEvent == strings.TrimSpace(fmt.Sprintf("%v\n", event)) {
+			donec <- true
+		}
+	}
+}