Fix rspec warnings

Spec threw warnings as raise_error didn’t provide an Error Class to
assert on. Indeed in one case the wrong error was raised than expected.

[fixes doorkeeper-gem#711]

spec/models/doorkeeper/access_token_spec.rb

@@ -123,17 +123,17 @@ module NoGenerate
       it 'is not valid if token exists' do
         token1 = FactoryGirl.create :access_token, use_refresh_token: true
         token2 = FactoryGirl.create :access_token, use_refresh_token: true
-        token2.send :write_attribute, :refresh_token, token1.refresh_token
+        token2.refresh_token = token1.refresh_token
         expect(token2).not_to be_valid
       end
 
       it 'expects database to raise an error if refresh tokens are the same' do
         token1 = FactoryGirl.create :access_token, use_refresh_token: true
         token2 = FactoryGirl.create :access_token, use_refresh_token: true
         expect do
-          token2.write_attribute :refresh_token, token1.refresh_token
+          token2.refresh_token = token1.refresh_token
           token2.save(validate: false)
-        end.to raise_error
+        end.to raise_error(ActiveRecord::RecordNotUnique)
       end
     end
 

spec/models/doorkeeper/application_spec.rb

@@ -90,7 +90,7 @@ module Doorkeeper
       app1 = FactoryGirl.create(:application)
       app2 = FactoryGirl.create(:application)
       app2.uid = app1.uid
-      expect { app2.save!(validate: false) }.to raise_error
+      expect { app2.save!(validate: false) }.to raise_error(ActiveRecord::RecordNotUnique)
     end
 
     it 'generate secret on create' do

spec/support/shared/models_shared_examples.rb

@@ -46,7 +46,7 @@
       token2.token = token1.token
       expect do
         token2.save!(validate: false)
-      end.to raise_error
+      end.to raise_error(ActiveRecord::RecordNotUnique)
     end
   end
 end