Add feature test for plugins on system hooks page

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

spec/features/admin/admin_hooks_spec.rb

@@ -24,6 +24,16 @@ describe 'Admin::Hooks' do
       visit admin_hooks_path
       expect(page).to have_content(system_hook.url)
     end
+
+    it 'renders plugins list as well' do
+      allow(Gitlab::Plugin).to receive(:files).and_return(['foo.rb', 'bar.clj'])
+
+      visit admin_hooks_path
+
+      expect(page).to have_content('Plugins')
+      expect(page).to have_content('foo.rb')
+      expect(page).to have_content('bar.clj')
+    end
   end
 
   describe 'New Hook' do