diff --git a/plugins/techdocs-backend/src/storage/BuildMetadataStorage.test.ts b/plugins/techdocs-backend/src/storage/BuildMetadataStorage.test.ts
new file mode 100644
index 0000000000..87de9d1d02
--- /dev/null
+++ b/plugins/techdocs-backend/src/storage/BuildMetadataStorage.test.ts
@@ -0,0 +1,27 @@
+/*
+ * Copyright 2020 Spotify AB
+ *
+ * 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.
+ */
+import { BuildMetadataStorage } from './BuildMetadataStorage';
+
+describe('BuildMetadataStorage', () => {
+  it('should return build timestamp', () => {
+    const newMetadataStorage = new BuildMetadataStorage('123abc');
+    newMetadataStorage.storeBuildTimestamp();
+
+    const timestamp = newMetadataStorage.getTimestamp();
+
+    expect(timestamp).toBeLessThanOrEqual(Date.now());
+  });
+});
diff --git a/plugins/techdocs-backend/src/storage/BuildMetadataStorage.ts b/plugins/techdocs-backend/src/storage/BuildMetadataStorage.ts
index b82ec1291a..d6a19764d9 100644
--- a/plugins/techdocs-backend/src/storage/BuildMetadataStorage.ts
+++ b/plugins/techdocs-backend/src/storage/BuildMetadataStorage.ts
@@ -20,6 +20,11 @@ type buildInfo = {
 
 const builds = {} as buildInfo;
 
+/**
+ * Store timestamps of the most recent TechDocs build of each Entity. This is
+ * used to invalidate cache if the latest commit in the documentation source
+ * repository is later than the timestamp.
+ */
 export class BuildMetadataStorage {
   public entityUid: string;
   private builds: buildInfo;