[java][bidi] Ensure removing listeners does not cause an error

Author: pujagani

java/src/org/openqa/selenium/bidi/BiDi.java

@@ -93,10 +93,14 @@ <X> void addListener(Set<String> browsingContextIds, Event<X> event, Consumer<X>
   public <X> void clearListener(Event<X> event) {
     Require.nonNull("Event to listen for", event);
 
-    send(new Command<>("session.unsubscribe",
-                       ImmutableMap.of("events", Collections.singletonList(event.getMethod()))));
-
-    connection.clearListener(event);
+    // The browser throws an error if we try to unsubscribe an event that was not subscribed in the first place
+    if (connection.isEventSubscribed(event)) {
+      send(new Command<>(
+        "session.unsubscribe",
+        ImmutableMap.of("events", Collections.singletonList(event.getMethod()))));
+
+      connection.clearListener(event);
+    }
   }
 
   public void clearListeners() {

java/src/org/openqa/selenium/bidi/Connection.java

@@ -188,6 +188,16 @@ public <X> void clearListener(Event<X> event) {
     }
   }
 
+  public <X> boolean isEventSubscribed(Event<X> event) {
+    Lock lock = callbacksLock.writeLock();
+    lock.lock();
+    try {
+      return eventCallbacks.containsKey(event);
+    } finally {
+      lock.unlock();
+    }
+  }
+
   public void clearListeners() {
     Lock lock = callbacksLock.writeLock();
     lock.lock();