add assertOps sanitizer in cli/js/ unit tests (#4209)

* add "assertOps" test assertion which makes sure test case
  is not "leaking" ops - ie. after test finishes there are no 
  pending async ops

* apply "assertOps" to all tests in "cli/js/"

* fix numerous tests leaking ops

* document problem with edge case in "clearInterval"
   and "clearTimeout" implementation where they
   may leak async ops

* move "cli/js/worker_test.ts" to "cli/tests/worker_test.ts" and 
  run as integration test; workers leak ops because of missing
  "terminate" implementation

1 files changed, 5 insertions, 2 deletions

diff --git a/cli/js/performance_test.ts b/cli/js/performance_test.ts
index 7e7f63d8c..227514954 100644
--- a/cli/js/performance_test.ts
+++ b/cli/js/performance_test.ts
@@ -1,10 +1,13 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-import { testPerm, assert } from "./test_util.ts";
+import { testPerm, assert, createResolvable } from "./test_util.ts";
 
-testPerm({ hrtime: false }, function now(): void {
+testPerm({ hrtime: false }, async function performanceNow(): Promise<void> {
+  const resolvable = createResolvable();
   const start = performance.now();
   setTimeout((): void => {
     const end = performance.now();
     assert(end - start >= 10);
+    resolvable.resolve();
   }, 10);
+  await resolvable;
 });