diff --git a/src/utils/index.test.ts b/src/utils/index.test.ts
new file mode 100644
index 00000000..57a41101
--- /dev/null
+++ b/src/utils/index.test.ts
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2020 The Pybricks Authors
+
+import { hex } from '.';
+
+test('hex', () => {
+    expect(hex(0, 2)).toBe('0x00');
+    expect(hex(1, 4)).toBe('0x0001');
+    expect(hex(2, 8)).toBe('0x00000002');
+});