denoland-deno/std/node/_fs/_fs_watch_test.ts

import { watch } from "./_fs_watch.ts";
import { assertEquals } from "../../testing/asserts.ts";

function wait(time: number) {
  return new Promise((resolve) => {
    setTimeout(resolve, time);
  });
}

Deno.test({
  name: "watching a file",
  async fn() {
    const file = Deno.makeTempFileSync();
    const result: Array<[string, string]> = [];
    const watcher = watch(
      file,
      (eventType, filename) => result.push([eventType, filename]),
    );
    await wait(100);
    Deno.writeTextFileSync(file, "something");
    await wait(100);
    watcher.close();
    assertEquals(result, [
      ["modify", file],
      ["modify", file],
      ["access", file],
    ]);
  },
});