Converted some left-over JavaScript file to TypeScript

Summary: Found some errors in a CI failure originating from a JavaScript file. The horror!

Reviewed By: jknoxville

Differential Revision: D29549998

fbshipit-source-id: 633100ec9a446050bb0c703dcc37e9b132b17198

desktop/app/src/utils/__tests__/icons.node.tsx

@@ -0,0 +1,35 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {buildLocalIconPath, buildIconURL} from '../icons';
+import * as path from 'path';
+
+test('filled icons get correct local path', () => {
+  const iconPath = buildLocalIconPath('star', 12, 2);
+  expect(iconPath).toBe(path.join('icons', 'star-filled-12@2x.png'));
+});
+
+test('outline icons get correct local path', () => {
+  const iconPath = buildLocalIconPath('star-outline', 12, 2);
+  expect(iconPath).toBe(path.join('icons', 'star-outline-12@2x.png'));
+});
+
+test('filled icons get correct URL', () => {
+  const iconUrl = buildIconURL('star', 12, 2);
+  expect(iconUrl).toBe(
+    'https://facebook.com/assets/?name=star&variant=filled&size=12&set=facebook_icons&density=2x',
+  );
+});
+
+test('outline icons get correct URL', () => {
+  const iconUrl = buildIconURL('star-outline', 12, 2);
+  expect(iconUrl).toBe(
+    'https://facebook.com/assets/?name=star&variant=outline&size=12&set=facebook_icons&density=2x',
+  );
+});