diff --git a/src/extensions/Stopwatch.test.ts b/src/extensions/Stopwatch.test.ts
new file mode 100644
index 00000000..35618314
--- /dev/null
+++ b/src/extensions/Stopwatch.test.ts
@@ -0,0 +1,54 @@
+import { describe, test } from "node:test";
+import assert from "node:assert/strict";
+import { Stopwatch, timePromise } from "./Stopwatch";
+
+describe("Stopwatch", () => {
+ test("should be able to be initialised", () => {
+ const sw = new Stopwatch();
+ assert.equal(sw != null, true);
+ });
+
+ test("should measure elapsed time", async () => {
+ const sw = Stopwatch.startNew();
+ await new Promise((resolve) => void setTimeout(resolve, 101));
+ sw.stop();
+ const elapsed = sw.elapsed();
+ assert(elapsed.totalMilliseconds >= 100, `Elapsed time was ${elapsed.totalMilliseconds} ms`);
+ });
+
+ test("should reset correctly", async () => {
+ const sw = Stopwatch.startNew();
+ await new Promise((resolve) => void setTimeout(resolve, 101));
+ sw.stop();
+ let elapsed = sw.elapsed();
+ assert(elapsed.totalMilliseconds >= 100, `Elapsed time was ${elapsed.totalMilliseconds} ms`);
+
+ sw.reset();
+ await new Promise((resolve) => void setTimeout(resolve, 50));
+ sw.stop();
+ elapsed = sw.elapsed();
+ assert(elapsed.totalMilliseconds >= 49 && elapsed.totalMilliseconds < 100, `Elapsed time after reset was ${elapsed.totalMilliseconds} ms`);
+ });
+
+ test("getElapsedAndReset should work correctly", async () => {
+ const sw = Stopwatch.startNew();
+ await new Promise((resolve) => void setTimeout(resolve, 101));
+ sw.stop();
+ let elapsed = sw.getElapsedAndReset();
+ assert(elapsed.totalMilliseconds >= 100, `Elapsed time was ${elapsed.totalMilliseconds} ms`);
+
+ await new Promise((resolve) => void setTimeout(resolve, 50));
+ sw.stop();
+ elapsed = sw.elapsed();
+ assert(elapsed.totalMilliseconds >= 50 && elapsed.totalMilliseconds < 100, `Elapsed time after getElapsedAndReset was ${elapsed.totalMilliseconds} ms`);
+ });
+
+ test("timePromise should measure promise execution time", async () => {
+ const { result, elapsed } = await timePromise(async () => {
+ await new Promise((resolve) => void setTimeout(resolve, 101));
+ return 42;
+ });
+ assert.equal(result, 42);
+ assert(elapsed.totalMilliseconds >= 100, `Elapsed time was ${elapsed.totalMilliseconds} ms`);
+ });
+});
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