improve deferred test (#5459)

1 files changed, 12 insertions, 3 deletions

diff --git a/std/async/deferred_test.ts b/std/async/deferred_test.ts
index 83c317853..c411885d0 100644
--- a/std/async/deferred_test.ts
+++ b/std/async/deferred_test.ts
@@ -1,8 +1,17 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { assertEquals, assertThrowsAsync } from "../testing/asserts.ts";
 import { deferred } from "./deferred.ts";
 
-Deno.test("[async] deferred", function (): Promise<void> {
+Deno.test("[async] deferred: resolve", async function (): Promise<void> {
+  const d = deferred<string>();
+  d.resolve("🦕");
+  assertEquals(await d, "🦕");
+});
+
+Deno.test("[async] deferred: reject", async function (): Promise<void> {
   const d = deferred<number>();
-  d.resolve(12);
-  return Promise.resolve();
+  d.reject(new Error("A deno error 🦕"));
+  await assertThrowsAsync(async () => {
+    await d;
+  });
 });