method Assert.prototype.async Assert.prototype.async(): () => void Returns a done callback for callback-style async tests. The test will not finish until every done callback returned by async() has been called. For async/await tests prefer async (assert) => { ... } directly. Examples Example 1 test("async callback style", (assert) => { const done = assert.async(); setTimeout(() => { assert.ok(true, "async callback ran"); done(); }, 10); }); Return Type () => void A callback to invoke when the async work finishes.