refactor(material-experimental/checkbox): change test for double-clicking

refactor the 'should not trigger the click event multiple times' test by
listening for changes on the parent of the mdc-checkbox rather than the
mdc-checkbox itself

Author: zarend

src/material-experimental/mdc-checkbox/checkbox.spec.ts

@@ -312,7 +312,7 @@ describe('MDC-based MatCheckbox', () => {
       // Since we're using a label element and a visual hidden input, this behavior can led
       // to an issue, where the click events on the checkbox are getting executed twice.
 
-      spyOn(testComponent, 'onCheckboxClick');
+      spyOn(testComponent, 'onParentElementClick');
 
       expect(inputElement.checked).toBe(false);
 
@@ -321,7 +321,7 @@ describe('MDC-based MatCheckbox', () => {
       flush();
 
       expect(inputElement.checked).toBe(true);
-      expect(testComponent.onCheckboxClick).toHaveBeenCalledTimes(1);
+      expect(testComponent.onParentElementClick).toHaveBeenCalledTimes(1);
     }));
 
     it('should trigger a change event when the native input does', fakeAsync(() => {
@@ -1034,7 +1034,7 @@ describe('MatCheckboxDefaultOptions', () => {
 /** Simple component for testing a single checkbox. */
 @Component({
   template: `
-  <div (click)="parentElementClicked = true" (keyup)="parentElementKeyedUp = true">
+  <div (click)="parentElementClicked = true; onParentElementClick($event)" (keyup)="parentElementKeyedUp = true">
     <mat-checkbox
         [id]="checkboxId"
         [required]="isRequired"
@@ -1066,6 +1066,7 @@ class SingleCheckbox {
 
   onCheckboxClick: (event?: Event) => void = () => {};
   onCheckboxChange: (event?: MatCheckboxChange) => void = () => {};
+  onParentElementClick: (event?: Event) => void = () => {};
 }
 
 /** Simple component for testing an MatCheckbox with required ngModel. */