newbie can't define a method in ruby for cucumber test pass

问题

I am trying to learn cucumber, here's an example code from a book:

class Output
  def messages
    @messages ||= []
  end

  def puts(message)
    messages << message
  end
end

def output
  @output ||= Output.new
end

Given /^I am not yet playing$/ do
end

When /^I start a new game$/ do
  game = Codebreaker::Game.new(output)
  game.start
end

Then /^I should see "([^"]*)"$/ do |message|
  output.messages.should include(message)
end

When I run this spec, I get this error:

  Scenario: start game                          # features/codebreaker_starts_game.feature:7
    Given I am not yet playing                  # features/step_definitions/codebreaker_steps.rb:15
    When I start a new game                     # features/step_definitions/codebreaker_steps.rb:18
    Then I should see "Welcome to Codebreaker!" # features/step_definitions/codebreaker_steps.rb:23
      undefined method `messages' for #<RSpec::Matchers::BuiltIn::Output:0xa86a7a4> (NoMethodError)
      ./features/step_definitions/codebreaker_steps.rb:24:in `/^I should see "([^"]*)"$/'
      features/codebreaker_starts_game.feature:10:in `Then I should see "Welcome to Codebreaker!"'
    And I should see "Enter guess:"             # features/step_definitions/codebreaker_steps.rb:23

See that it gives undefined method 'messages' error, yet it is defined in the Output class.

If I replace output.messages.should with Output.new.messages.should, it works fine. What is the problem here?

Edit: Probably output is a keyword, in new version of rails, when I changed it to outputz it worked fine. An explanation of this will be accepted as an answer.

回答1:

Apparently, the output matcher has been added to rspec in version 3.0:

The output matcher provides a way to assert that the has emitted content to either $stdout or $stderr.

With no arg, passes if the block outputs to_stdout or to_stderr. With a string, passes if the blocks outputs that specific string to_stdout or to_stderr. With a regexp or matcher, passes if the blocks outputs a string to_stdout or to_stderr that matches.

Examples:

RSpec.describe "output.to_stdout matcher" do
  specify { expect { print('foo') }.to output.to_stdout }
  specify { expect { print('foo') }.to output('foo').to_stdout }
  specify { expect { print('foo') }.to output(/foo/).to_stdout }
  specify { expect { }.to_not output.to_stdout }
  specify { expect { print('foo') }.to_not output('bar').to_stdout }
  specify { expect { print('foo') }.to_not output(/bar/).to_stdout }

来源：https://stackoverflow.com/questions/26850871/newbie-cant-define-a-method-in-ruby-for-cucumber-test-pass