Added unit test.

Signed-off-by: Du Zheng <zsuzhengdu@gmail.com>

pkg/reloader/reloader.go

@@ -197,6 +197,11 @@ func (r *Reloader) Watch(ctx context.Context) error {
 		}
 	}
 
+	if r.watchInterval == 0 {
+		// Skip watching the file-system
+		return nil
+	}
+
 	for _, dir := range r.watchedDirs {
 		if err := r.watcher.addDirectory(dir); err != nil {
 			return errors.Wrapf(err, "add directory %s to watcher", dir)
@@ -291,11 +296,6 @@ func (r *Reloader) apply(ctx context.Context) error {
 			if err := os.Rename(tmpFile, r.cfgOutputFile); err != nil {
 				return errors.Wrap(err, "rename file")
 			}
-
-			if r.watchInterval == 0 {
-				<-ctx.Done()
-				return nil
-			}
 		}
 	}
 

pkg/reloader/reloader_test.go

@@ -501,3 +501,93 @@ func TestReloaderDirectoriesApplyBasedOnWatchInterval(t *testing.T) {
 	testutil.Ok(t, err)
 	testutil.Equals(t, 2, reloads.Load().(int))
 }
+
+func TestReloader_ConfigApplyWithWatchIntervalEqualsZero(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Minute)
+	defer cancel()
+
+	l, err := net.Listen("tcp", "localhost:0")
+	testutil.Ok(t, err)
+
+	reloads := &atomic.Value{}
+	reloads.Store(0)
+	i := 0
+	srv := &http.Server{}
+	srv.Handler = http.HandlerFunc(func(resp http.ResponseWriter, r *http.Request) {
+		i++
+		if i%2 == 0 {
+			// Every second request, fail to ensure that retry works.
+			resp.WriteHeader(http.StatusServiceUnavailable)
+			return
+		}
+
+		reloads.Store(reloads.Load().(int) + 1) // The only writer.
+		resp.WriteHeader(http.StatusOK)
+	})
+	go func() { _ = srv.Serve(l) }()
+	defer func() { testutil.Ok(t, srv.Close()) }()
+
+	reloadURL, err := url.Parse(fmt.Sprintf("http://%s", l.Addr().String()))
+	testutil.Ok(t, err)
+
+	dir, err := ioutil.TempDir("", "reloader-cfg-test")
+	testutil.Ok(t, err)
+	defer func() { testutil.Ok(t, os.RemoveAll(dir)) }()
+
+	testutil.Ok(t, os.Mkdir(filepath.Join(dir, "in"), os.ModePerm))
+	testutil.Ok(t, os.Mkdir(filepath.Join(dir, "out"), os.ModePerm))
+
+	var (
+		input  = filepath.Join(dir, "in", "cfg.yaml.tmpl")
+		output = filepath.Join(dir, "out", "cfg.yaml")
+	)
+	reloader := New(nil, nil, &Options{
+		ReloadURL:     reloadURL,
+		CfgFile:       input,
+		CfgOutputFile: output,
+		WatchedDirs:   nil,
+		WatchInterval: 0, // Set WatchInterval equals to 0
+		RetryInterval: 100 * time.Millisecond,
+		DelayInterval: 1 * time.Millisecond,
+	})
+
+	testutil.Ok(t, ioutil.WriteFile(input, []byte(`
+config:
+  a: 1
+  b: 2
+  c: 3
+`), os.ModePerm))
+
+	rctx, cancel2 := context.WithCancel(ctx)
+	g := sync.WaitGroup{}
+	g.Add(1)
+	go func() {
+		defer g.Done()
+		testutil.Ok(t, reloader.Watch(rctx))
+	}()
+
+	for {
+		select {
+		case <-ctx.Done():
+			fmt.Println("cancelled")
+			break
+		case <-time.After(300 * time.Millisecond):
+			fmt.Println("timeout")
+		}
+
+		if reloads.Load().(int) == 1 {
+			// Initial apply seen (without doing nothing).
+			f, err := ioutil.ReadFile(output)
+			testutil.Ok(t, err)
+			testutil.Equals(t, `
+config:
+  a: 1
+  b: 2
+  c: 3
+`, string(f))
+			break
+		}
+	}
+	cancel2()
+	g.Wait()
+}