Rename mock connection interface

Rename inbox to messages to be more consistent

spec/support/mock_connection.rb

@@ -1,17 +1,15 @@
 class MockConnection
   def initialize
-    @inbox = []
+    @messages = []
   end
 
   def send(message)
-    @inbox.push(message)
+    @messages.push(message)
   end
 
-  def messages
-    @inbox
-  end
+  attr_reader :messages
 
-  def clear_inbox!
-    @inbox = []
+  def clear_messages!
+    @messages = []
   end
 end