user mailers

completes #25

test/controllers/admin/user_controller_test.rb

@@ -28,9 +28,11 @@ module Admin
     end
 
     test "should post create" do
-      assert_difference("User.count", 1) do
-        post admin_create_user_url, params: { user:
-            { email: 'new.user@mailinator.com', name: 'New User', role: 'reviewer' } }
+      assert_difference("ActionMailer::Base.deliveries.size", 1) do
+        assert_difference("User.count", 1) do
+          post admin_create_user_url, params: { user:
+              { email: 'new.user@mailinator.com', name: 'New User', role: 'reviewer' } }
+        end
       end
       assert_redirected_to admin_users_url
     end