diff --git a/utils.test.ts b/utils.test.ts
new file mode 100644
index 0000000..25bb59f
--- /dev/null
+++ b/utils.test.ts
@@ -0,0 +1,22 @@
+import { expect, test, spyOn } from "bun:test"
+import { arrayOfLength, arrayShuffle } from './utils';
+
+test('arrayOfLength', () => {
+  expect(arrayOfLength(3)).toHaveLength(3)
+})
+
+test('arrayShuffle', () => {
+  spyOn(global.Math, 'random').mockReturnValue(0.123);
+
+  const unshuffled = [1, 2, 3]
+  const shuffled = arrayShuffle(unshuffled)
+
+  expect(shuffled.includes(unshuffled[0])).toBe(true)
+  expect(shuffled.includes(unshuffled[1])).toBe(true)
+  expect(shuffled.includes(unshuffled[2])).toBe(true)
+  expect(shuffled[0]).not.toBe(unshuffled[0])
+  expect(shuffled[1]).not.toBe(unshuffled[1])
+  expect(shuffled[2]).not.toBe(unshuffled[2])
+
+  spyOn(global.Math, 'random').mockRestore();
+}, { repeats: 9 })