Instance Eval'd blocks for ActionDispatch::Integration::Runner#open_session

test_helper.rb

class ActionDispatch::IntegrationTest
  # Override Rails open_session so we can use an instance involved block
  # instead of passing the session instance and using it. This allows the block
  # to work exactly the same as the regular test.
  def open_session(&block)
    return super if block.nil? || block.arity > 0
    super do |session|
      session.instance_eval(&block)
    end
  end

  # Helper method for login that uses the instance_eval'd block
  def login(email, password = 'password')
    open_session do
      post sessions_url, params: { email: email, password: password }
      assert_response :success, "Unable to login for #{email}:#{password}"
      yield if block_given?
    end
  end
end

user_controller_test_after.rb

# This is what the test looks like with the instance_eval'd block
class UsersControllerTest < ActionDispatch::IntegrationTest
  test 'Staff can show a user' do
    user = users(:staff)
    login(user.email) do
      get user_url(id: users(:user).id)
      assert_response :success
    end
  end
end

user_controller_test_before.rb

# This is what the test and helper look like with the regular session argument block, 
# while it is arguably not significantly more complicated it is inconsistent with any
# test code that is written outside of an open_session block.
class UsersControllerTest < ActionDispatch::IntegrationTest
    def login(email, password = 'password')
    open_session do |session|
      session.post sessions_url, params: { email: email, password: password }
      session.assert_response :success, "Unable to login for #{email}:#{password}"
      yield session if block_given?
    end
  end
  
  test 'Staff can show a user' do
    user = users(:staff)
    login(user.email) do |session|
      session.get user_url(id: users(:user).id)
      session.assert_response :success
    end
  end
end

Obviously in an actually implementation you would just change the implementation ActionDispatch::Integration::Runner#open_session. But for the purpose of doing this in test_helper.rb I decided to just override it in the test base class.