Write tests for hooks

Signed-off-by: Emma Indal <emma.indahl@gmail.com>
Co-authored-by: Camila Belo <camilaibs@gmail.com>

plugins/techdocs-addons/src/hooks.test.ts

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+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * 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 { useShadowRoot, useShadowRootElements } from './hooks';
+import { renderHook } from '@testing-library/react-hooks';
+
+const mockShadowRoot = () => {
+  const div = document.createElement('div');
+  const shadowRoot = div.attachShadow({ mode: 'open' });
+  shadowRoot.innerHTML = '<h1>Shadow DOM Mock</h1>';
+  return shadowRoot;
+};
+
+const shadowRoot = mockShadowRoot();
+
+jest.mock('./context', () => {
+  return {
+    useTechDocsReaderPage: () => ({ shadowRoot }),
+  };
+});
+
+describe('hooks', () => {
+  describe('useShadowRoot', () => {
+    it('should return shadow root', async () => {
+      const { result } = renderHook(() => useShadowRoot());
+
+      expect(result.current?.innerHTML).toBe(shadowRoot.innerHTML);
+    });
+  });
+
+  describe('useShadowRootElements', () => {
+    it('should return shadow root elements based on selector', () => {
+      const { result } = renderHook(() => useShadowRootElements(['h1']));
+
+      expect(result.current).toHaveLength(1);
+    });
+  });
+});