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.
