diff --git a/plugins/techdocs/src/reader/transformers/onCssReady.test.ts b/plugins/techdocs/src/reader/transformers/onCssReady.test.ts
new file mode 100644
index 0000000000..10edbbae5e
--- /dev/null
+++ b/plugins/techdocs/src/reader/transformers/onCssReady.test.ts
@@ -0,0 +1,87 @@
+/*
+ * 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 {
+  FIXTURES,
+  createTestShadowDom,
+  mockStylesheetEventListener,
+  executeStylesheetEventListeners,
+  clearStylesheetEventListeners,
+} from '../../test-utils';
+import { addBaseUrl, onCssReady } from '../transformers';
+
+const docStorageURL: string =
+  'https://techdocs-mock-sites.storage.googleapis.com';
+
+jest.useFakeTimers();
+
+describe('onCssReady', () => {
+  beforeEach(() => {
+    mockStylesheetEventListener(100);
+  });
+
+  afterEach(() => {
+    clearStylesheetEventListeners();
+  });
+
+  it('does not call onLoading and onLoaded without the addBaseUrl transformer', () => {
+    const onLoading = jest.fn();
+    const onLoaded = jest.fn();
+
+    createTestShadowDom(FIXTURES.FIXTURE_STANDARD_PAGE, {
+      transformers: [
+        onCssReady({
+          docStorageURL,
+          onLoading,
+          onLoaded,
+        }),
+      ],
+    });
+
+    expect(onLoading).not.toHaveBeenCalled();
+    executeStylesheetEventListeners();
+    expect(onLoaded).not.toHaveBeenCalled();
+  });
+
+  it('calls the onLoading and onLoaded correctly', () => {
+    const onLoading = jest.fn();
+    const onLoaded = jest.fn();
+
+    createTestShadowDom(FIXTURES.FIXTURE_STANDARD_PAGE, {
+      transformers: [
+        addBaseUrl({
+          docStorageURL,
+          componentId: 'mkdocs',
+          path: '',
+        }),
+        onCssReady({
+          docStorageURL,
+          onLoading,
+          onLoaded,
+        }),
+      ],
+    });
+
+    expect(onLoading).toHaveBeenCalledTimes(1);
+    expect(onLoading).toHaveBeenCalledWith(expect.any(Element));
+    expect(onLoaded).not.toHaveBeenCalled();
+
+    executeStylesheetEventListeners();
+
+    expect(onLoaded).toHaveBeenCalledTimes(1);
+    expect(onLoaded).toHaveBeenCalledWith(expect.any(Element));
+  });
+});