Raise an exception when trying to subscribe to an unregister event

lib/dry/events/bus.rb

@@ -76,6 +76,11 @@ def subscribe(event_id, query, &block)
       def subscribed?(listener)
         listeners.values.any? { |value| value.any? { |(block, _)| block.equal?(listener) } }
       end
+
+      # @api private
+      def register_event?(event_id)
+        events.keys.any? { |value| value == event_id }
+      end
     end
   end
 end

lib/dry/events/publisher.rb

@@ -18,6 +18,14 @@ def initialize(id)
       end
     end
 
+    # @api public
+    UnregisterEventError = Class.new(StandardError) do
+      # @api private
+      def initialize(event_id)
+        super("you are trying to subscribe to an event: #{event_id} that has not been register")
+      end
+    end
+
     # Extension used for classes that can publish events
     #
     # @example
@@ -189,6 +197,7 @@ def publish(event_id, payload = EMPTY_HASH)
         #
         # @api public
         def subscribe(object_or_event_id, query = EMPTY_HASH, &block)
+          raise UnregisterEventError, object_or_event_id unless registered_event?(object_or_event_id)
           if block
             __bus__.subscribe(object_or_event_id, query, &block)
           else
@@ -236,6 +245,20 @@ def process(event_id, payload = EMPTY_HASH, &block)
         def __bus__
           @__bus__ ||= self.class.new_bus
         end
+
+        # Utility method that check that the event has been registered
+        #
+        # @return [Boolean]
+        #
+        # @api private
+        def registered_event?(object_or_event_id)
+          case object_or_event_id
+          when String, Symbol
+            __bus__.register_event?(object_or_event_id)
+          else
+            true
+          end
+        end
       end
     end
   end

spec/unit/dry/events/publisher_spec.rb

@@ -39,6 +39,14 @@
 
       expect(publisher.subscribed?(listener)).to be(true)
     end
+
+    it 'raises an exception when subscribing to an unregister event' do
+      listener = -> * { }
+
+      expect {
+        publisher.subscribe(:not_register, &listener)
+      }.to raise_error(Dry::Events::UnregisterEventError, /not_register/)
+    end
   end
 
   describe '#register_event' do