Tests , assertion output value always <>

no problem running my tests ( units , functionals ) but when
assertion failed , I never see any assertion output value, it’s always
<> and expected also is <>

i.e. :

=> 33: assert ability.can? :index, User
34: get :index
35: assert_response :success
36: assert_not_nil assigns(:users)
<> expected but was
<>

I must have some wrong parameter , but where ? any clue welcome…

group :test do
gem ‘single_test’
gem ‘simplecov’
gem ‘fakeweb’
gem ‘autotest-rails’
end