Merge pull request #1465 from prometheus/beorn7/fix-test2

Fix flaky file-sd test

retrieval/discovery/file_test.go

@@ -59,11 +59,17 @@ func testFileSD(t *testing.T, ext string) {
 	}
 	newf.Close()
 
+	timeout := time.After(15 * time.Second)
 	// The files contain two target groups.
+retry:
+	for {
 		select {
-	case <-time.After(15 * time.Second):
+		case <-timeout:
 			t.Fatalf("Expected new target group but got none")
 		case tgs := <-ch:
+			if len(tgs) != 2 {
+				continue retry // Potentially a partial write, just retry.
+			}
 			tg := tgs[0]
 
 			if _, ok := tg.Labels["foo"]; !ok {
@@ -77,6 +83,8 @@ func testFileSD(t *testing.T, ext string) {
 			if tg.String() != fmt.Sprintf("fixtures/_test%s:1", ext) {
 				t.Fatalf("Unexpected target groups %s", tg)
 			}
+			break retry
+		}
 	}
 
 	// Based on unknown circumstances, sometimes fsnotify will trigger more events in