Dark theme for calling device selection

ts/test-both/util/theme_test.ts

@@ -0,0 +1,16 @@
+// Copyright 2019-2020 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+
+import { Theme, themeClassName } from '../../util/theme';
+
+describe('themeClassName', () => {
+  it('returns "light-theme" when passed a light theme', () => {
+    assert.strictEqual(themeClassName(Theme.Light), 'light-theme');
+  });
+
+  it('returns "dark-theme" when passed a dark theme', () => {
+    assert.strictEqual(themeClassName(Theme.Dark), 'dark-theme');
+  });
+});