test(core): Wait for zone stability before test completion (#55468)

Need to wait for microtaskEmty to emit or test will leak into others.

PR Close #55468

packages/core/test/zone/ng_zone_spec.ts

@@ -9,6 +9,7 @@
 import {EventEmitter, NgZone} from '@angular/core';
 import {fakeAsync, flushMicrotasks, inject, waitForAsync} from '@angular/core/testing';
 import {Log} from '@angular/core/testing/src/testing_internal';
+import {firstValueFrom} from 'rxjs';
 
 import {scheduleCallbackWithRafRace as scheduler} from '../../src/util/callback_scheduler';
 import {global} from '../../src/util/global';
@@ -1193,10 +1194,13 @@ function commonTests() {
  });
  });
 
- it('does not throw when apply args array has `undefined`', () => {
+ it('does not throw when apply args array has `undefined`', async () => {
  expect(() => {
  coalesceZone.run(function(this: any, arg: any) {}, undefined, [undefined]);
  }).not.toThrow();
+ // wait for the zone to stabilize after the task above. Needed to prevent this from leaking
+ // into a follow-up test
+ await firstValueFrom(coalesceZone.onMicrotaskEmpty);
  });
  });
  });