Bug: Performance issue

[lneumeier-visma]

Description of the bug

ngMocks.flushTestBed() function prevents the cleanup-code in angular's TestBed.tearDownTestingModule function. As a result, unit test execution is much slower, because of duplicated, not cleaned up shared host styles (and maybe other objects). (3000 tests, 3-4 minutes instead of 1-1,5 minutes)

An example of the bug

ngMocks.flushTestBed() called from https://github.com/help-me-mom/ng-mocks/blob/master/libs/ng-mocks/src/lib/common/ng-mocks-global-overrides.ts#L56 sets the _testModuleRef to null
(https://github.com/help-me-mom/ng-mocks/blob/master/libs/ng-mocks/src/lib/mock-helper/mock-helper.flush-test-bed.ts#L7)

This prevents the cleanup of the test module.
https://github.com/angular/angular/blob/main/packages/core/testing/src/test_bed.ts#L735

  // If the module ref has already been destroyed, we won't be able to get a test renderer.
    if (this._testModuleRef === null) {
      return;
    }
    // Resolve the renderer ahead of time, because we want to remove the root elements as the very
    // last step, but the injector will be destroyed as a part of the module ref destruction.
    const testRenderer = this.inject(TestComponentRenderer);
    try {
      this._testModuleRef.destroy();
    } catch (e) {
      if (this.shouldRethrowTeardownErrors()) {
        throw e;
      } else {
        console.error('Error during cleanup of a testing module', {
          component: this._testModuleRef.instance,
          stacktrace: e,
        });
      }
    } finally {
      testRenderer.removeAllRootElements?.();
    }

Link:

Expected vs actual behavior

Workaround tests.ts:
Add

afterEach(() => { getTestBed().inject(ɵSharedStylesHost).ngOnDestroy(); });

angular/angular#31834 (comment)

Possible fix in ng-mocks (mock-helper.flush-test-bed.ts)

export default (): void => {
  const testBed: any = getTestBed();
  testBed.tearDownTestingModule(); // run cleanup
  testBed._instantiated = false;
  testBed._moduleFactory = undefined;
  testBed._testModuleRef = null;
};