diff --git a/test/common/string/get_duplicate.test.ts b/test/common/string/get_duplicate.test.ts
new file mode 100644
index 0000000000..821e5d8a74
--- /dev/null
+++ b/test/common/string/get_duplicate.test.ts
@@ -0,0 +1,16 @@
+import { expect, test } from "vitest";
+import { getDuplicates } from "../../../src/common/string/get_duplicates";
+
+test("getDuplicate", () => {
+  expect(getDuplicates([])).toStrictEqual(new Set());
+  expect(getDuplicates(["light", "vacuum", "switch"])).toStrictEqual(new Set());
+  expect(getDuplicates(["light", "light", "vacuum", "switch"])).toStrictEqual(
+    new Set(["light"])
+  );
+  expect(
+    getDuplicates(["vacuum", "light", "light", "vacuum", "switch"])
+  ).toStrictEqual(new Set(["light", "vacuum"]));
+  expect(getDuplicates(["light", "light", "light"])).toStrictEqual(
+    new Set(["light"])
+  );
+});