diff --git a/apps/app/src/lib/__tests__/util.test.ts b/apps/app/src/lib/__tests__/util.test.ts
new file mode 100644
index 00000000..2aff587c
--- /dev/null
+++ b/apps/app/src/lib/__tests__/util.test.ts
@@ -0,0 +1,22 @@
+import { deepExtendRemovingUndefined } from '../util'
+
+test('deepExtendRemovingUndefined', () => {
+	{
+		const target = {
+			a: 1,
+		}
+		deepExtendRemovingUndefined(target, {
+			b: 2,
+		})
+		expect(target).toStrictEqual({ a: 1, b: 2 })
+	}
+	{
+		const target = {
+			a: [1, 2, 3],
+		}
+		deepExtendRemovingUndefined(target, {
+			a: [4, 5, 6],
+		})
+		expect(target).toStrictEqual({ a: [4, 5, 6] })
+	}
+})