test 'should success sign-up and print success flash message' do
    request_params = {
      user: {
        first_name: 'Test',
        last_name: 'Test',
        email: 'example@test.com',
        password: 'password',
        password_confirmation: 'password'
      }
    }

    post user_registration_path(request_params)

    assert_redirected_to root_path

    follow_redirect!
    follow_redirect!

    assert_select(flash_message_container, text: 'Welcome! You have signed up successfully.')
end

private

def flash_message_container
  '.flash-message-content'
end