This was fixed in mongoid, closes #770.

test/models/token_authenticatable_test.rb

@@ -27,12 +27,6 @@ class TokenAuthenticatableTest < ActiveSupport::TestCase
   end
 
   test 'should return nil when authenticating an invalid user by authentication token' do
-    if DEVISE_ORM == :mongoid
-      raise 'There is an incompatibility between Devise and Mongoid'  <<
-            ' that makes this test break. For more information, check' <<
-            ' this issue: https://github.com/mongoid/mongoid/issues/725'
-    end
-
     user = create_user
     user.ensure_authentication_token!
     user.confirm!