Respond with 406 if we can't return requested formats

lib/travis/api/app/helpers/respond_with.rb

@@ -24,12 +24,14 @@ class Travis::Api::App
         def respond(resource, options)
           resource = apply_service_responder(resource, options)
 
-          acceptable_formats.find do |accept|
+          response = acceptable_formats.find do |accept|
             responders(resource, options).find do |const|
               responder = const.new(self, resource, options.dup.merge(accept: accept))
               responder.apply if responder.apply?
             end
           end
+
+          response || (resource ? error(406) : error(404))
         end
 
         def apply_service_responder(resource, options)

spec/integration/formats_handling_spec.rb

@@ -24,4 +24,9 @@ describe 'App' do
     response = get '/foo', {}, 'HTTP_ACCEPT' => 'image/jpeg, application/json'
     response.content_type.should =~ /^application\/json/
   end
+
+  it 'responds with 406 if server can\'t use any mime type' do
+    response = get '/foo/hash', {}, 'HTTP_ACCEPT' => 'text/plain, image/jpeg'
+    response.status.should == 406
+  end
 end