added test go implementation

network-go/watcher/watcher_test.go

@@ -0,0 +1,179 @@
+package watcher
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestWatcherDetectsChange(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "test.json")
+	if err := os.WriteFile(path, []byte(`{"version": 1}`), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	changeDetected := make(chan bool, 1)
+	onChange := func() {
+		select {
+		case changeDetected <- true:
+		default:
+		}
+	}
+
+	fw := NewFileWatcher(path, 100*time.Millisecond, onChange)
+	fw.Start()
+	defer fw.Stop()
+
+	// Wait for initial hash to be computed
+	time.Sleep(200 * time.Millisecond)
+
+	// Modify the file
+	if err := os.WriteFile(path, []byte(`{"version": 2}`), 0644); err != nil {
+		t.Fatalf("failed to modify test file: %v", err)
+	}
+
+	// Wait for change detection
+	select {
+	case detected := <-changeDetected:
+		if !detected {
+			t.Error("expected change detection, got false")
+		}
+	case <-time.After(2 * time.Second):
+		t.Error("timeout waiting for file change detection")
+	}
+}
+
+func TestWatcherNoChange(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "test.json")
+	if err := os.WriteFile(path, []byte(`{"version": 1}`), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	changeDetected := make(chan bool, 1)
+	onChange := func() {
+		select {
+		case changeDetected <- true:
+		default:
+		}
+	}
+
+	fw := NewFileWatcher(path, 100*time.Millisecond, onChange)
+	fw.Start()
+	defer fw.Stop()
+
+	// Wait without modifying the file
+	time.Sleep(300 * time.Millisecond)
+
+	// Should not detect a change
+	select {
+	case <-changeDetected:
+		t.Error("unexpected change detection without file modification")
+	default:
+		// Expected: no change detected
+	}
+}
+
+func TestWatcherMultipleChanges(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "test.json")
+	if err := os.WriteFile(path, []byte(`{"v": 1}`), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	changeCount := 0
+	var mu chan struct{}
+
+	onChange := func() {
+		changeCount++
+		if mu != nil {
+			mu <- struct{}{}
+		}
+	}
+
+	fw := NewFileWatcher(path, 50*time.Millisecond, onChange)
+	fw.Start()
+	defer fw.Stop()
+
+	// Wait for initial hash
+	time.Sleep(100 * time.Millisecond)
+
+	// Make 3 changes
+	for i := 2; i <= 4; i++ {
+		if err := os.WriteFile(path, []byte(`{"v": `+string(rune('0'+i))+`}`), 0644); err != nil {
+			t.Fatalf("failed to modify file: %v", err)
+		}
+		time.Sleep(150 * time.Millisecond)
+	}
+
+	if changeCount < 2 {
+		t.Errorf("expected at least 2 change detections, got %d", changeCount)
+	}
+}
+
+func TestWatcherStop(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "test.json")
+	if err := os.WriteFile(path, []byte(`{"v": 1}`), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	fw := NewFileWatcher(path, 50*time.Millisecond, func() {})
+	fw.Start()
+
+	time.Sleep(100 * time.Millisecond)
+	fw.Stop()
+
+	// Should not panic on double stop or further operations
+	time.Sleep(100 * time.Millisecond)
+}
+
+func TestWatcherNonexistentFile(t *testing.T) {
+	onChange := func() {
+		t.Error("onChange should not be called for nonexistent file")
+	}
+
+	fw := NewFileWatcher("/nonexistent/file.json", 100*time.Millisecond, onChange)
+	fw.Start()
+	defer fw.Stop()
+
+	// Wait — should not call onChange since file doesn't exist
+	time.Sleep(300 * time.Millisecond)
+}
+
+func TestWatcherReproducible(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "test.json")
+	if err := os.WriteFile(path, []byte(`{"data": "value"}`), 0644); err != nil {
+		t.Fatalf("failed to write test file: %v", err)
+	}
+
+	// Create two watchers on the same file
+	var detected1, detected2 bool
+
+	fw1 := NewFileWatcher(path, 50*time.Millisecond, func() { detected1 = true })
+	fw2 := NewFileWatcher(path, 50*time.Millisecond, func() { detected2 = true })
+
+	fw1.Start()
+	fw2.Start()
+	defer fw1.Stop()
+	defer fw2.Stop()
+
+	time.Sleep(100 * time.Millisecond)
+
+	// Modify file
+	if err := os.WriteFile(path, []byte(`{"data": "changed"}`), 0644); err != nil {
+		t.Fatalf("failed to modify file: %v", err)
+	}
+
+	time.Sleep(300 * time.Millisecond)
+
+	if !detected1 {
+		t.Error("watcher 1 did not detect change")
+	}
+	if !detected2 {
+		t.Error("watcher 2 did not detect change")
+	}
+}