Break ThemeChoicePanel into a separate component (#6998)

* Break ThemeChoicePanel into a separate component

* Tests for ThemeChoicePanel

* i18n fixes

* Fix copyright for ThemeChoicePanel

test/components/views/settings/ThemeChoicePanel-test.tsx

@@ -0,0 +1,60 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+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 React from 'react';
+import { mount } from "enzyme";
+
+import '../../../skinned-sdk';
+import * as TestUtils from "../../../test-utils";
+import _ThemeChoicePanel from '../../../../src/components/views/settings/ThemeChoicePanel';
+
+const ThemeChoicePanel = TestUtils.wrapInMatrixClientContext(_ThemeChoicePanel);
+
+// Avoid errors about global.matchMedia. See:
+// https://jestjs.io/docs/manual-mocks#mocking-methods-which-are-not-implemented-in-jsdom
+Object.defineProperty(window, 'matchMedia', {
+    writable: true,
+    value: jest.fn().mockImplementation(query => ({
+        matches: false,
+        media: query,
+        onchange: null,
+        addListener: jest.fn(), // Deprecated
+        removeListener: jest.fn(), // Deprecated
+        addEventListener: jest.fn(),
+        removeEventListener: jest.fn(),
+        dispatchEvent: jest.fn(),
+    })),
+});
+
+// Fake random strings to give a predictable snapshot
+jest.mock(
+    'matrix-js-sdk/src/randomstring',
+    () => {
+        return {
+            randomString: () => "abdefghi",
+        };
+    },
+);
+
+describe('ThemeChoicePanel', () => {
+    it('renders the theme choice UI', () => {
+        TestUtils.stubClient();
+        const wrapper = mount(
+            <ThemeChoicePanel />,
+        );
+        expect(wrapper).toMatchSnapshot();
+    });
+});