refactor: cleanup fake event dispatch utilities (angular#19151)

Cleans up the fake event dispatch utiltities:

1. `dispatchMouseEvent` accepts an actual mouse event. This has been
introduced with [this commit](04bf3d1).
If a mouse event has already been created, then it can be just
dispatched, but doesn't need to go through `dispatchMouseEvent` which
primarily is a shorthand for creating an event and dispatching it.

2. `dispatchEvent` helper should use a generic so that we don't
need to cast events unnecessarily.

3. `createMouseEvent` should not accept `x` and `y`. This is ambiguous.
It's not clear what coordinates are expected. To improve this,
parameters are now explicit, and a better comment has been added.

src/cdk/testing/testbed/fake-events/dispatch-events.ts

@@ -18,7 +18,7 @@ import {
  * Utility to dispatch any event on a Node.
  * @docs-private
  */
-export function dispatchEvent(node: Node | Window, event: Event): Event {
+export function dispatchEvent<T extends Event>(node: Node | Window, event: T): T {
   node.dispatchEvent(event);
   return event;
 }
@@ -38,16 +38,15 @@ export function dispatchFakeEvent(node: Node | Window, type: string, canBubble?:
 export function dispatchKeyboardEvent(node: Node, type: string, keyCode?: number, key?: string,
                                       target?: Element, modifiers?: ModifierKeys): KeyboardEvent {
   return dispatchEvent(node,
-      createKeyboardEvent(type, keyCode, key, target, modifiers)) as KeyboardEvent;
+      createKeyboardEvent(type, keyCode, key, target, modifiers));
 }
 
 /**
  * Shorthand to dispatch a mouse event on the specified coordinates.
  * @docs-private
  */
-export function dispatchMouseEvent(node: Node, type: string, x = 0, y = 0,
-  event = createMouseEvent(type, x, y)): MouseEvent {
-  return dispatchEvent(node, event) as MouseEvent;
+export function dispatchMouseEvent(node: Node, type: string, clientX = 0, clientY = 0): MouseEvent {
+  return dispatchEvent(node, createMouseEvent(type, clientX, clientY));
 }
 
 /**

src/cdk/testing/testbed/fake-events/event-objects.ts

@@ -12,25 +12,32 @@ import {ModifierKeys} from '@angular/cdk/testing';
  * Creates a browser MouseEvent with the specified options.
  * @docs-private
  */
-export function createMouseEvent(type: string, x = 0, y = 0, button = 0) {
+export function createMouseEvent(type: string, clientX = 0, clientY = 0, button = 0) {
   const event = document.createEvent('MouseEvent');
   const originalPreventDefault = event.preventDefault.bind(event);
 
+  // Note: We cannot determine the position of the mouse event based on the screen
+  // because the dimensions and position of the browser window are not available
+  // To provide reasonable `screenX` and `screenY` coordinates, we simply use the
+  // client coordinates as if the browser is opened in fullscreen.
+  const screenX = clientX;
+  const screenY = clientY;
+
   event.initMouseEvent(type,
-    true, /* canBubble */
-    true, /* cancelable */
-    window, /* view */
-    0, /* detail */
-    x, /* screenX */
-    y, /* screenY */
-    x, /* clientX */
-    y, /* clientY */
-    false, /* ctrlKey */
-    false, /* altKey */
-    false, /* shiftKey */
-    false, /* metaKey */
-    button, /* button */
-    null /* relatedTarget */);
+    /* canBubble */ true,
+    /* cancelable */ true,
+    /* view */ window,
+    /* detail */ 0,
+    /* screenX */ screenX,
+    /* screenY */ screenY,
+    /* clientX */ clientX,
+    /* clientY */ clientY,
+    /* ctrlKey */ false,
+    /* altKey */ false,
+    /* shiftKey */ false,
+    /* metaKey */ false,
+    /* button */ button,
+    /* relatedTarget */ null);
 
   // `initMouseEvent` doesn't allow us to pass the `buttons` and
   // defaults it to 0 which looks like a fake event.

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

@@ -2035,7 +2035,7 @@ describe('MDC-based MatMenu', () => {
       Object.defineProperty(event, 'buttons', {get: () => 1});
       event.preventDefault = jasmine.createSpy('preventDefault spy');
 
-      dispatchMouseEvent(overlay.querySelector('[mat-menu-item]')!, 'mousedown', 0, 0, event);
+      dispatchEvent(overlay.querySelector('[mat-menu-item]')!, event);
       expect(event.preventDefault).toHaveBeenCalled();
     });
 

src/material/menu/menu.spec.ts

@@ -10,8 +10,8 @@ import {
   dispatchFakeEvent,
   dispatchKeyboardEvent,
   dispatchMouseEvent,
-  patchElementFocus,
   MockNgZone,
+  patchElementFocus,
 } from '@angular/cdk/testing/private';
 import {
   ChangeDetectionStrategy,
@@ -2031,7 +2031,7 @@ describe('MatMenu', () => {
       Object.defineProperty(event, 'buttons', {get: () => 1});
       event.preventDefault = jasmine.createSpy('preventDefault spy');
 
-      dispatchMouseEvent(overlay.querySelector('[mat-menu-item]')!, 'mousedown', 0, 0, event);
+      dispatchEvent(overlay.querySelector('[mat-menu-item]')!, event);
       expect(event.preventDefault).toHaveBeenCalled();
     });