fix(common): prevent duplicate URL change notifications (#37459)

Prevent duplicate notifications from being emitted when multiple URL change listeners are registered using SpyLocation#onUrlChange.

Use `@internal` annotation for the `_urlChangeSubscription` properties instead of the `private` access modifier. Otherwise, we get in trouble because of  `SpyLocation implements Location`.

PR Close #37459

Author: LayZeeDK

packages/common/src/location/location.ts

@@ -64,7 +64,8 @@ export class Location {
   _platformLocation: PlatformLocation;
   /** @internal */
   _urlChangeListeners: ((url: string, state: unknown) => void)[] = [];
-  private _urlChangeSubscription?: SubscriptionLike;
+  /** @internal */
+  _urlChangeSubscription?: SubscriptionLike;
 
   constructor(platformStrategy: LocationStrategy, platformLocation: PlatformLocation) {
     this._platformStrategy = platformStrategy;

packages/common/testing/src/location_mock.ts

@@ -30,6 +30,8 @@ export class SpyLocation implements Location {
   _platformLocation: PlatformLocation = null!;
   /** @internal */
   _urlChangeListeners: ((url: string, state: unknown) => void)[] = [];
+  /** @internal */
+  _urlChangeSubscription?: SubscriptionLike;
 
   setInitialPath(url: string) {
     this._history[this._historyIndex].path = url;
@@ -123,9 +125,12 @@ export class SpyLocation implements Location {
   }
   onUrlChange(fn: (url: string, state: unknown) => void) {
     this._urlChangeListeners.push(fn);
-    this.subscribe(v => {
-      this._notifyUrlChangeListeners(v.url, v.state);
-    });
+
+    if (!this._urlChangeSubscription) {
+      this._urlChangeSubscription = this.subscribe(v => {
+        this._notifyUrlChangeListeners(v.url, v.state);
+      });
+    }
   }
 
   /** @internal */