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, 28 insertions, 2 deletions

diff --git a/cli/js/test_util.ts b/cli/js/test_util.ts
index 6f52c01df..027610dd9 100644
--- a/cli/js/test_util.ts
+++ b/cli/js/test_util.ts
@@ -107,10 +107,36 @@ function normalizeTestPermissions(perms: TestPermissions): Permissions {
 }
 
 // Wrap `TestFunction` in additional assertion that makes sure
+// the test case does not leak async "ops" - ie. number of async
+// completed ops after the test is the same as number of dispatched
+// ops. Note that "unref" ops are ignored since in nature that are
+// optional.
+function assertOps(fn: Deno.TestFunction): Deno.TestFunction {
+  return async function asyncOpSanitizer(): Promise<void> {
+    const pre = Deno.metrics();
+    await fn();
+    const post = Deno.metrics();
+    // We're checking diff because one might spawn HTTP server in the background
+    // that will be a pending async op before test starts.
+    assertEquals(
+      post.opsDispatchedAsync - pre.opsDispatchedAsync,
+      post.opsCompletedAsync - pre.opsCompletedAsync,
+      `Test case is leaking async ops.
+    Before:
+      - dispatched: ${pre.opsDispatchedAsync}
+      - completed: ${pre.opsCompletedAsync}
+    After: 
+      - dispatched: ${post.opsDispatchedAsync}
+      - completed: ${post.opsCompletedAsync}`
+    );
+  };
+}
+
+// Wrap `TestFunction` in additional assertion that makes sure
 // the test case does not "leak" resources - ie. resource table after
 // the test has exactly the same contents as before the test.
 function assertResources(fn: Deno.TestFunction): Deno.TestFunction {
-  return async function(): Promise<void> {
+  return async function resourceSanitizer(): Promise<void> {
     const preResources = Deno.resources();
     await fn();
     const postResources = Deno.resources();
@@ -131,7 +157,7 @@ export function testPerm(perms: TestPermissions, fn: Deno.TestFunction): void {
     return;
   }
 
-  Deno.test(fn.name, assertResources(fn));
+  Deno.test(fn.name, assertResources(assertOps(fn)));
 }
 
 export function test(fn: Deno.TestFunction): void {