test: add UT for filewatcher

pkg/filewatcher/filewatcher.go

@@ -25,6 +25,11 @@ import (
 	"k8s.io/klog/v2"
 )
 
+// exit is a separate function to handle program termination
+var exit = func(code int) {
+	os.Exit(code)
+}
+
 var watchCertificateFileOnce sync.Once
 
 // WatchFileForChanges watches the file, fileToWatch, for changes. If the file contents have changed, the pod this
@@ -44,9 +49,7 @@ func WatchFileForChanges(fileToWatch string) error {
 		klog.V(2).Infof("Watching file, %s", fileToWatch)
 
 		// Start the file watcher to monitor file changes
-		go func() {
-			err = checkForFileChanges(fileToWatch)
-		}()
+		err = checkForFileChanges(fileToWatch)
 	})
 	return err
 }
@@ -64,7 +67,7 @@ func checkForFileChanges(path string) error {
 			case event, ok := <-watcher.Events:
 				if ok && (event.Has(fsnotify.Write) || event.Has(fsnotify.Chmod) || event.Has(fsnotify.Remove)) {
 					klog.V(2).Infof("file, %s, was modified, exiting...", event.Name)
-					os.Exit(0)
+					exit(0)
 				}
 			case err, ok := <-watcher.Errors:
 				if ok {

pkg/filewatcher/filewatcher_test.go

@@ -0,0 +1,50 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package filewatcher
+
+import (
+	"os"
+	"testing"
+	"time"
+)
+
+func TestWatchFileForChanges(t *testing.T) {
+	// Set mock exit once.
+	exit = func(_ int) {
+		// Mock, do nothing
+	}
+
+	// Create a temporary file to watch
+	tmpfile, err := os.CreateTemp("", "testfile")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(tmpfile.Name())
+
+	// Now call the watcher
+	if err = WatchFileForChanges(tmpfile.Name()); err != nil {
+		t.Errorf("Failed to watch file: %v", err)
+	}
+
+	// Trigger the watcher
+	if err = os.WriteFile(tmpfile.Name(), []byte("new content"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	// Let the watcher see the change
+	time.Sleep(1 * time.Second)
+}