[GH-847] Add unit tests for contentElement (#1501)

* chore[GH-#847]: add unit tests for contentElement

* fix: checkbox not need...

* fix: checkbox not need...

webapp/src/components/content/__snapshots__/contentElement.test.tsx.snap

@@ -0,0 +1,22 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`components/content/contentElement return an element 1`] = `
+<div>
+  <div
+    class="CheckboxElement"
+  >
+    <input
+      id="checkbox-test-id"
+      type="checkbox"
+      value="off"
+    />
+    <input
+      class="Editable undefined"
+      placeholder="Edit text..."
+      spellcheck="true"
+      title="test-title"
+      value="test-title"
+    />
+  </div>
+</div>
+`;

webapp/src/components/content/contentElement.test.tsx

@@ -0,0 +1,52 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+import {render} from '@testing-library/react'
+
+import {wrapIntl} from '../../testUtils'
+
+import {ContentBlock} from '../../blocks/contentBlock'
+
+import ContentElement from './contentElement'
+
+describe('components/content/contentElement', () => {
+    test('return an element', () => {
+        const contentBlock: ContentBlock = {
+            id: 'test-id',
+            workspaceId: '',
+            parentId: '',
+            rootId: '',
+            modifiedBy: 'test-user-id',
+            schema: 0,
+            type: 'checkbox',
+            title: 'test-title',
+            fields: {},
+            createdBy: 'test-user-id',
+            createAt: 0,
+            updateAt: 0,
+            deleteAt: 0,
+        }
+        const checkBoxElement = ContentElement({block: contentBlock, readonly: false})
+        const {container} = render(wrapIntl(checkBoxElement))
+        expect(container).toMatchSnapshot()
+    })
+
+    test('return null', () => {
+        const contentBlock: ContentBlock = {
+            id: 'test-id',
+            workspaceId: '',
+            parentId: '',
+            rootId: '',
+            modifiedBy: 'test-user-id',
+            schema: 0,
+            type: 'unknown',
+            title: 'test-title',
+            fields: {},
+            createdBy: 'test-user-id',
+            createAt: 0,
+            updateAt: 0,
+            deleteAt: 0,
+        }
+        const contentElement = ContentElement({block: contentBlock, readonly: false})
+        expect(contentElement).toBeNull()
+    })
+})