diff --git a/pkg/tarfs/tarfs.go b/pkg/tarfs/tarfs.go
index 90382c1f68..87256e80be 100755
--- a/pkg/tarfs/tarfs.go
+++ b/pkg/tarfs/tarfs.go
@@ -179,6 +179,7 @@ func (t *Manager) fetchImageConfig(ctx context.Context, remote *remote.Remote, r
 	return config, nil
 }
 
+// <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
 func (t *Manager) getBlobDiffID(ctx context.Context, remote *remote.Remote, ref string, manifestDigest, layerDigest digest.Digest) (digest.Digest, error) {
 	if diffid, ok := t.diffIDCache.Get(layerDigest); ok {
 		return diffid.(digest.Digest), nil
@@ -444,6 +445,8 @@ func (t *Manager) retryPrepareLayer(snapshotID, upperDirPath string, labels map[
 	return nil
 }
 
+// >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
+
 func (t *Manager) PrepareLayer(snapshotID, ref string, manifestDigest, layerDigest digest.Digest, upperDirPath string) error {
 	t.mutex.Lock()
 	if _, ok := t.snapshotMap[snapshotID]; ok {
@@ -465,6 +468,7 @@ func (t *Manager) PrepareLayer(snapshotID, ref string, manifestDigest, layerDige
 	return t.blobProcess(ctx, snapshotID, ref, manifestDigest, layerDigest, upperDirPath, false)
 }
 
+// <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
 func (t *Manager) MergeLayers(ctx context.Context, s storage.Snapshot, storageLocater func(string) string,
 	infoGetter func(ctx context.Context, id string) (string, snapshots.Info, error)) error {
 	mergedBootstrap := t.imageMetaFilePath(storageLocater(s.ParentIDs[0]))
@@ -939,6 +943,8 @@ func (t *Manager) RecoverRafsInstance(r *rafs.Rafs) error {
 	return nil
 }
 
+// >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
+
 func (t *Manager) getSnapshotStatusWithLock(snapshotID string) (*snapshotStatus, error) {
 	t.mutex.Lock()
 	defer t.mutex.Unlock()
diff --git a/pkg/tarfs/tarfs_test.go b/pkg/tarfs/tarfs_test.go
new file mode 100644
index 0000000000..cad6fcb68e
--- /dev/null
+++ b/pkg/tarfs/tarfs_test.go
@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2023. Nydus Developers. All rights reserved.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package tarfs
+
+import (
+	"context"
+	"testing"
+
+	"github.com/containerd/continuity/testutil"
+	"github.com/containerd/nydus-snapshotter/pkg/label"
+	"github.com/containerd/nydus-snapshotter/pkg/rafs"
+	"github.com/opencontainers/go-digest"
+	"gotest.tools/assert"
+)
+
+const (
+	BusyboxRef            = "quay.io/quay/busybox@sha256:92f3298bf80a1ba949140d77987f5de081f010337880cd771f7e7fc928f8c74d"
+	BusyboxManifestDigest = "sha256:92f3298bf80a1ba949140d77987f5de081f010337880cd771f7e7fc928f8c74d"
+	BusyboxLayerDigest    = "sha256:ee780d08a5b4de5192a526d422987f451d9a065e6da42aefe8c3b20023a250c7"
+)
+
+func TestPrepareLayer(t *testing.T) {
+	manager := NewManager(true, true, "/tmp/tarfs", "/usr/bin/nydus-image", 4)
+	manifestDigest, err := digest.Parse(BusyboxManifestDigest)
+	assert.Assert(t, err)
+	layerDigest, err := digest.Parse(BusyboxLayerDigest)
+	assert.Assert(t, err)
+
+	err = manager.PrepareLayer("snapshot1", BusyboxRef, manifestDigest, layerDigest, t.TempDir())
+	assert.Assert(t, err)
+
+	// snapshot, err := manager.waitLayerReady("snapshot1", true)
+	// assert.Assert(t, err)
+	// assert.Equal(t, snapshot.blobID, "ee780d08a5b4de5192a526d422987f451d9a065e6da42aefe8c3b20023a250c7")
+
+	err = manager.PrepareLayer("snapshot1", BusyboxRef, manifestDigest, layerDigest, t.TempDir())
+	assert.Assert(t, err != nil)
+}
+
+func TestCheckTarfsHintAnnotation(t *testing.T) {
+	manager := NewManager(true, true, "/tmp/tarfs", "/usr/bin/nydus-image", 4)
+	ctx := context.Background()
+	hint, err := manager.CheckTarfsHintAnnotation(ctx, BusyboxRef, BusyboxManifestDigest)
+	assert.Assert(t, err)
+	assert.Equal(t, hint, false)
+}
+
+func TestGetConcurrentLimiter(t *testing.T) {
+	manager := NewManager(false, false, "/tmp/tarfs", "/usr/bin/nydus-image", 4)
+	limiter := manager.GetConcurrentLimiter("busybox")
+	assert.Assert(t, limiter != nil)
+	assert.Equal(t, manager.GetConcurrentLimiter("busybox"), limiter)
+
+}
+
+func TestCopyTarfsAnnotations(t *testing.T) {
+	manager := NewManager(false, false, "/tmp/tarfs", "/usr/bin/nydus-image", 4)
+	rafs := &rafs.Rafs{
+		Annotations: make(map[string]string),
+	}
+
+	annotations := map[string]string{}
+	annotations[label.CRIImageRef] = "cri_image_ref"
+	annotations[label.CRILayerDigest] = "cri_layer_digest"
+	annotations[label.CRIManifestDigest] = "cri_manigest_digest"
+	annotations[label.NydusTarfsLayer] = "nydus_tarfs_layer"
+	annotations[label.NydusImageBlockInfo] = "nydus_image_block_info"
+	annotations[label.NydusLayerBlockInfo] = "nydus_layer_block_info"
+	annotations["unsupported_key"] = "error"
+
+	manager.copyTarfsAnnotations(annotations, rafs)
+	assert.Equal(t, len(rafs.Annotations), 6)
+	assert.Equal(t, rafs.Annotations[label.CRIImageRef], annotations[label.CRIImageRef])
+	assert.Equal(t, rafs.Annotations[label.CRILayerDigest], annotations[label.CRILayerDigest])
+}
+
+func TestTarfsFilePath(t *testing.T) {
+	manager := NewManager(false, false, "/tmp/tarfs", "/usr/bin/nydus-image", 4)
+
+	assert.Equal(t, manager.layerTarFilePath("blob1"), "/tmp/tarfs/blob1")
+	assert.Equal(t, manager.layerDiskFilePath("blob1"), "/tmp/tarfs/blob1.layer.disk")
+	assert.Equal(t, manager.ImageDiskFilePath("blob1"), "/tmp/tarfs/blob1.image.disk")
+	assert.Equal(t, manager.layerMetaFilePath("/tarfs/fs"), "/tarfs/fs/image/layer.boot")
+	assert.Equal(t, manager.imageMetaFilePath("/tarfs/fs"), "/tarfs/fs/image/image.boot")
+}
+
+func TestTarfsStatusString(t *testing.T) {
+	assert.Equal(t, tarfsStatusString(TarfsStatusReady), "Ready")
+	assert.Equal(t, tarfsStatusString(TarfsStatusPrepare), "Prepare")
+	assert.Equal(t, tarfsStatusString(TarfsStatusFailed), "Failed")
+	assert.Equal(t, tarfsStatusString(4), "Unknown")
+}
+
+func TestAttachBlob(t *testing.T) {
+	testutil.RequiresRoot(t)
+
+	manager := NewManager(false, false, "/tmp/tarfs", "/usr/bin/nydus-image", 4)
+	blobFile := createTempFile(t)
+	loopdev, err := manager.attachLoopdev(blobFile)
+	assert.Assert(t, err)
+	err = deleteLoop(loopdev)
+	assert.Assert(t, err)
+	err = deleteLoop(loopdev)
+	assert.Assert(t, err != nil)
+}