fix(common): Fix MockPlatformLocation events and missing onPopState i…

…mplementation (#48113)

The MockPlatformLocation forward, back, and historyGo methods should trigger a popstate event.
Additionally, these events should just be synchronous since that's what the majority of the major
browsers do. Lastly, onPopState should be implemented the same way as onHashChange.

PR Close #48113

packages/common/testing/src/mock_platform_location.ts

@@ -105,6 +105,7 @@ export const MOCK_PLATFORM_LOCATION_CONFIG =
 export class MockPlatformLocation implements PlatformLocation {
   private baseHref: string = '';
   private hashUpdate = new Subject<LocationChangeEvent>();
+  private popStateSubject = new Subject<LocationChangeEvent>();
   private urlChangeIndex: number = 0;
   private urlChanges: {
     hostname: string,
@@ -155,9 +156,8 @@ export class MockPlatformLocation implements PlatformLocation {
   }
 
   onPopState(fn: LocationChangeListener): VoidFunction {
-    // No-op: a state stack is not implemented, so
-    // no events will ever come.
-    return () => {};
+    const subscription = this.popStateSubject.subscribe(fn);
+    return () => subscription.unsubscribe();
   }
 
   onHashChange(fn: LocationChangeListener): VoidFunction {
@@ -204,7 +204,7 @@ export class MockPlatformLocation implements PlatformLocation {
     if (this.urlChangeIndex < this.urlChanges.length) {
       this.urlChangeIndex++;
     }
-    this.scheduleHashUpdate(oldHash, oldUrl);
+    this.emitEvents(oldHash, oldUrl);
   }
 
   back(): void {
@@ -213,7 +213,7 @@ export class MockPlatformLocation implements PlatformLocation {
     if (this.urlChangeIndex > 0) {
       this.urlChangeIndex--;
     }
-    this.scheduleHashUpdate(oldHash, oldUrl);
+    this.emitEvents(oldHash, oldUrl);
   }
 
   historyGo(relativePosition: number = 0): void {
@@ -223,22 +223,30 @@ export class MockPlatformLocation implements PlatformLocation {
     if (nextPageIndex >= 0 && nextPageIndex < this.urlChanges.length) {
       this.urlChangeIndex = nextPageIndex;
     }
-    this.scheduleHashUpdate(oldHash, oldUrl);
+    this.emitEvents(oldHash, oldUrl);
   }
 
   getState(): unknown {
     return this.state;
   }
 
-  private scheduleHashUpdate(oldHash: string, oldUrl: string) {
+  /**
+   * Browsers are inconsistent in when they fire events and perform the state updates
+   * The most easiest thing to do in our mock is synchronous and that happens to match
+   * Firefox and Chrome, at least somewhat closely
+   *
+   * https://github.com/WICG/navigation-api#watching-for-navigations
+   * https://docs.google.com/document/d/1Pdve-DJ1JCGilj9Yqf5HxRJyBKSel5owgOvUJqTauwU/edit#heading=h.3ye4v71wsz94
+   * popstate is always sent before hashchange:
+   * https://developer.mozilla.org/en-US/docs/Web/API/Window/popstate_event#when_popstate_is_sent
+   */
+  private emitEvents(oldHash: string, oldUrl: string) {
+    this.popStateSubject.next(
+        {type: 'popstate', state: this.getState(), oldUrl, newUrl: this.url} as
+        LocationChangeEvent);
     if (oldHash !== this.hash) {
-      scheduleMicroTask(
-          () => this.hashUpdate.next(
-              {type: 'hashchange', state: null, oldUrl, newUrl: this.url} as LocationChangeEvent));
+      this.hashUpdate.next(
+          {type: 'hashchange', state: null, oldUrl, newUrl: this.url} as LocationChangeEvent);
     }
   }
 }
-
-export function scheduleMicroTask(cb: () => any) {
-  Promise.resolve().then(cb);
-}