Small Issues with Rails 5 and RSpec, Capybara. April 22, 2016
For error: email already taken run bundle exec rails db:test:prepare cleans the db so you can run your tests again without them failing.
For error: nomethoderror for expect(response).to render_template... for running tests in your controller specs. Install gem 'rails-controller-testing' and go into your rails_helper.rb and write the following code RSpec.configure do |config|
end This will allow controller testing within your rails 5 project without erroring out.
Refer to the Github