Add simple default message on receiving an unknown command

Author: tdmalone

src/events.js

@@ -168,7 +168,12 @@ const handlers = {
       return appCommandHandlers[appCommand]( event, request );
     }
 
-    return false;
+    const defaultMessage = (
+      'Sorry, I\'m not quite sure what you\'re asking me. I\'m not very smart - there\'s only a ' +
+      'few things I\'ve been trained to do. Send me `help` for more details.'
+    );
+
+    return slack.sendMessage( defaultMessage, event.channel );
 
   } // AppMention event.
 }; // Handlers.

tests/events.js

@@ -197,15 +197,6 @@ describe( 'handlers.appMention', () => {
 
   });
 
-  it( 'returns false if a supported command cannot be found', () => {
-    const event = {
-      type: eventType,
-      text: '<@U00000000> some_command_that_should_not_exist'
-    };
-
-    expect( handlers.appMention( event ) ).toBeFalse();
-  });
-
 }); // Handlers.appMention.
 
 describe( 'handleEvent', () => {