test(async/unstable): fix flaky waitFor() test (#6413)

Author: timreichen

async/unstable_wait_for_test.ts

@@ -1,28 +1,27 @@
 // Copyright 2018-2025 the Deno authors. MIT license.
-import { assertAlmostEquals, assertEquals, assertRejects } from "@std/assert";
+import { assertEquals, assertLess, assertRejects } from "@std/assert";
 import { waitFor } from "./unstable_wait_for.ts";
 
 // NOT detecting leaks means that the internal interval was correctly cleared
 
 Deno.test("waitFor() returns fulfilled promise", async () => {
   let flag = false;
   setTimeout(() => flag = true, 100);
-  const start = Date.now();
+  const start = performance.now();
   await waitFor(() => flag === true, 1000);
-  // Expects the promise to be resolved after 100ms
-  assertAlmostEquals(Date.now() - start, 100, 10);
+  assertLess(performance.now() - start, 1000);
 });
 
 Deno.test("waitFor() throws DOMException on timeout", async () => {
   let flag = false;
   const id = setTimeout(() => flag = true, 1000);
-  const start = Date.now();
+  const start = performance.now();
   const error = await assertRejects(
     () => waitFor(() => flag === true, 100),
     DOMException,
     "Signal timed out.",
   );
-  assertAlmostEquals(Date.now() - start, 100, 10);
+  assertLess(performance.now() - start, 1000);
   assertEquals(error.name, "TimeoutError");
   clearTimeout(id);
 });