This release features a sexier Double definition block syntax using instance_eval:

mock(User) do
  find(1) {user_1}
  find(2) {user_2}
end

RR also maintains its non-instance_evaled Double definition block syntax, if the block has an arity of 1:

mock(User) do |expect|
  expect.find(1) {user_1}
  expect.find(2) {user_2}
end

The instance_eval syntax is very useful in the context of Double Definition chaining:

mock.proxy(User).find(1) do
  mock.proxy! do
    blogs do
      mock.proxy!.find_by_id(2) do |actual_blog|
        actual_blog.name.should == "My ranty blog"
        actual_blog
      end
    end

    fans do
      mock.proxy!.thank_everybody
    end

    foes do
      mock.proxy!.ask_for_forgiveness
    end
  end
end

user = User.find(1)
user.blogs.find_by_id(2) # My ranty blog
user.fans.thank_everybody
user.foes.ask_for_forgiveness

Of course the previous example is a complicated case of interaction testing, and a simpler state-based and/or hybrid approach may be better, but it demonstrates how using instance_eval can promote readability.

Here is the non-instance_eval solution:

mock.proxy(User).find(1) do
  mock.proxy! do |expect|
    expect.blogs do
      mock.proxy!.find_by_id(2) do |actual_blog|
        actual_blog.name.should == "My ranty blog"
        actual_blog
      end
    end

    expect.fans do
      mock.proxy!.thank_everybody
    end

    expect.foes do
      mock.proxy!.ask_for_forgiveness
    end
  end
end

instance_eval Controversy

Ola Bini warned against overusing instance_eval. While instance_eval adds beauty, it can also make things more difficult to extend and debug.

In RR, the DoubleDefinitionCreatorProxy (the object that is instance_evaled when defining Doubles using blocks) uses the blank slate pattern, so arbitrary method names can be passed in to define the Double. The Blank Slate implies that the DoubleDefinitionCreatorProxy will not be extended with methods. James Earl Gray explains the pattern that I used for RR.

spec/test helper methods will not be usable within the instance_evaled blocks because the intent of the DoubleDefinitionCreatorProxy object is incompatible with the instance_eval with delegation pattern. DoubleDefinitionCreatorProxy already uses method_missing to create DoubleDefinitions. If you wish to use spec/test helper methods, you will need to memoize it to a variable and use lexical scoping.

Now, one may want to define a helper method in the test/spec that is returned when the Double is invoked.

describe User do
  describe "#fans.thank_everybody" do
    it "thanks all of my lovely fans" do
      user = User.new
      memoized_my_lovely_fans = my_lovely_fans
      mock(user) {fans {memoized_my_lovely_fans}}
      memoized_my_lovely_fans.each {|fan| mock(fan).thank_you}

      user.fans.thank_everybody
    end

    def my_lovely_fans
      [Fan.new, Fan.new]
    end
  end
end

While I think this will be a good addition to RR, I recognize that adding the instance_eval has the possibility of making RR less usable. I’ll pay close attention to see how this pans out and am willing to remove it if there are major issues.

About the Author

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