Add unit tests for BlobEnumerator

Signed-off-by: Guillaume Rose <guillaume.rose@docker.com>

registry/storage/paths_test.go

@@ -83,6 +83,10 @@ func TestPathMapper(t *testing.T) {
 			},
 			expected: "/docker/registry/v2/repositories/foo/bar/_uploads/asdf-asdf-asdf-adsf/startedat",
 		},
+		{
+			spec:     layersPathSpec{name: "foo/bar"},
+			expected: "/docker/registry/v2/repositories/foo/bar/_layers",
+		},
 	} {
 		p, err := pathFor(testcase.spec)
 		if err != nil {