05.3.txt

5.3  Green: Get the Example to Pass

The failure message tells us that output never received puts. Here’s what we need to do to get this example to pass:

Download cb/10/lib/codebreaker/game.rb

module Codebreaker
	class Game
		def initialize(output)
			@output = output
		end

		def start
			@output.puts 'Welcome to Codebreaker!'
		end 
	end
end

Make those changes and run the rspec command again, and you should see this:

Codebreaker::Game
	#start
		sends a welcome message
		prompts for the first guess (PENDING: Not Yet Implemented)

Pending:
	Codebreaker::Game#start prompts for the first guess
		# Not Yet Implemented
		# ./spec/codebreaker/game_spec.rb:14

Finished in 0.00144 seconds
2 examples, 0 failures, 1 pending

We have our first passing example! We’ve gone from red to green. The next step in the cycle is to refactor. We don’t really have any duplication yet, so let’s see whether we’ve had any impact on the features:

Scenario: start game
	Given I am not yet playing
	When I start a new game
	Then I should see "Welcome to Codebreaker!"
	And I should see "Enter guess:"
		expected ["Welcome to Codebreaker!"] to include "Enter guess:"

Progress!  Now  one  of  the  two  Thens  is  passing,  so  it  looks  like  we’re about halfway done with this feature. Actually, we’re quite a bit more than  halfway  done,  because,  as  you’ll  soon  see,  all  the  pieces  are  al- ready in place for the rest.
 


Next Step

The  following  failing  step  is  the  next  thing  to  work  on:  And  I  should see “Enter guess:”.  Go  ahead  and  add  an  example  for  this  behavior  to game_spec.rb:

Download cb/11/spec/codebreaker/game_spec.rb

require 'spec_helper'

module Codebreaker 
	describe Game do
		describe "#start" do
			it "sends a welcome message" do
				output = double('output')
				game = Game.new(output)

				output.should_receive(:puts).with('Welcome to Codebreaker!')

				game.start
			end

			it "prompts for the first guess" do
				output = double('output')
				game = Game.new(output)

				output.should_receive(:puts).with('Enter guess:')

				game.start
			end 
		end
	end 
end

This is very similar to the first example, but we’re expecting a different message. We’ll come back and DRY that up in a bit, but first let’s get it passing. Run the spec, and watch it fail:

Codebreaker::Game
	#start
		sends a welcome message
		prompts for the first guess (FAILED - 1)

Failures:
1) Codebreaker::Game#start prompts for the first guess
	Failure/Error: game.start
		Double "output" received :puts with unexpected arguments 
			expected: ("Enter guess:")
				got: ("Welcome to Codebreaker!")
			# ./lib/codebreaker/game.rb:8:in `start'
			# ./spec/codebreaker/game_spec.rb:22

Finished in 0.00199 seconds
2 examples, 1 failure
 


This  time,  the  output  didn’t  receive  puts('Enter guess:').  Resolve  that  as follows:

Download cb/12/lib/codebreaker/game.rb

module Codebreaker
	class Game
		def initialize(output)
			@output = output
		end

		def start
			@output.puts 'Welcome to Codebreaker!'
			@output.puts 'Enter guess:'
		end 
	end
end

Run the rspec command:

Codebreaker::Game
	#start
		sends a welcome message (FAILED - 1)
		prompts for the first guess (FAILED - 2)

Failures:
	1) Codebreaker::Game#start sends a welcome message
		Failure/Error: game.start
		Double "output" received :puts with unexpected arguments
			expected: ("Welcome to Codebreaker!")
				 got: ("Enter guess:")
		# ./lib/codebreaker/game.rb:10:in `start'
		# ./spec/codebreaker/game_spec.rb:12

	2) Codebreaker::Game#start prompts for the first guess
		Failure/Error: game.start
		Double "output" received :puts with unexpected arguments
			expected: ("Enter guess:")
				 got: ("Welcome to Codebreaker!")
		# ./lib/codebreaker/game.rb:8:in `start'
		# ./spec/codebreaker/game_spec.rb:21

Finished in 0.00219 seconds
2 examples, 2 failures

And ta-da! Now not only is the second example still failing, but the first example is failing as well! Who’da thunk? This may seem a bit confusing if you’ve never worked with test doubles and message expectations before,  but  test  doubles  are  like  computers.  They  are  extraordinarily obedient,  but  they  are  not  all  that  clever.  By  default,  they will  expect exactly what you tell them to expect, nothing more and nothing less.

We’ve told the double in the first example to expect puts( ) with “Welcome to Codebreaker!” and we’ve satisfied that requirement, but we’ve only told  it  to  expect  “Welcome  to  Codebreaker!”  It  doesn’t  know  anything about “Enter guess:”

Similarly, the double in the second example expects “Enter guess:” but the first message it gets is “Welcome to Codebreaker!”

We could combine these two into a single example, but we like to follow the guideline of “one expectation per example.” The rationale here is  that  if  there  are  two  expectations  in  an  example  that  should both fail  given  the  implementation  at  that  moment,  we’ll  only  see  the  first failure. No sooner do we meet that expectation than we discover that we haven’t met the second expectation. If they live in separate examples, then they’ll both fail, and that will provide us with more accurate 
information than if only one of them is failing.

We  could  also  try  to  break  the  messages  up  into  different  steps,  but we’ve already defined how we want to talk to the game object. So, how can we resolve this?

as_null_object

There are a couple of ways we can go about it, but the simplest way is to tell the double output to only listen for the messages we tell it to expect and ignore any other messages.3  This is based on the Null Object design pattern described in Pattern Languages of Program Design 3 [MRB97] and is supported by RSpec’s double framework with the as_null_object( ) method:

Download cb/13/spec/codebreaker/game_spec.rb

require 'spec_helper'

module Codebreaker describe 
	Game do
		describe "#start" do
			it "sends a welcome message" do
				output = double('output').as_null_object game = Game.new(output)

				output.should_receive(:puts).with('Welcome to Codebreaker!')

				game.start
			end
		 
			it "prompts for the first guess" do
				output = double('output').as_null_object game = Game.new(output)

				output.should_receive(:puts).with('Enter guess:')

				game.start
			end 
		end
	end
end

3.  Actually,  that’s  not  completely  true.  Unexpected  messages  are  actually  recorded because it is sometimes helpful to include them in failure messages.

Run the rspec command again, and you should see this:

Codebreaker::Game
	#start
		sends a welcome message 
		prompts for the first guess

Finished in 0.00174 seconds
2 examples, 0 failures

Good news. Both examples are now passing. Now that we have green, it’s time to refactor!