diff --git a/internal/graph/graph_test.go b/internal/graph/graph_test.go
index 5f6cc7bf6..599307fa2 100644
--- a/internal/graph/graph_test.go
+++ b/internal/graph/graph_test.go
@@ -121,7 +121,7 @@ func TestReferrers(t *testing.T) {
 		index
 	)
 	anno := map[string]string{"test": "foo"}
-	appendBlob(ocispec.MediaTypeArtifactManifest, []byte("subject content"))
+	appendBlob(ocispec.MediaTypeArtifactManifest, []byte(`{"name":"subject content"}`))
 	imageType := "test.image"
 	appendBlob(imageType, []byte("config content"))
 	generateImage(nil, nil, descs[imgConfig], descs[blob])
@@ -246,7 +246,7 @@ func TestSuccessors(t *testing.T) {
 		artifact
 		index
 	)
-	appendBlob(ocispec.MediaTypeArtifactManifest, []byte("subject content"))
+	appendBlob(ocispec.MediaTypeArtifactManifest, []byte(`{"name":"subject content"}`))
 	imageType := "test.image"
 	appendBlob(imageType, []byte("config content"))
 	generateImage(&descs[subject], ocispec.MediaTypeImageManifest, descs[config])
@@ -345,7 +345,7 @@ func TestFindReferrerPredecessors(t *testing.T) {
 		image
 	)
 	var anno map[string]string
-	appendBlob(ocispec.MediaTypeArtifactManifest, []byte("subject content"))
+	appendBlob(ocispec.MediaTypeArtifactManifest, []byte(`{"name":"subject content"}`))
 	imageType := "test.image"
 	appendBlob(imageType, []byte("config content"))
 	generateImage(&descs[subject], anno, descs[imgConfig])
@@ -373,7 +373,6 @@ func TestFindReferrerPredecessors(t *testing.T) {
 		want    []ocispec.Descriptor
 		wantErr bool
 	}{
-
 		{"should failed to get referrers", args{ctx, &errLister{}, ocispec.Descriptor{}}, nil, true},
 		{"should failed to get predecessor", args{ctx, &errFinder{}, ocispec.Descriptor{}}, nil, true},
 		{"should return referrers when target is a referrer lister", args{ctx, &refLister{referrers: referrers}, ocispec.Descriptor{}}, referrers, false},