Question

This may be a naive question, but does RSpec’s testing DSL violate the law of Demeter?

Here’s an example of the RSpec DSL from http://rspec.info:

bowling.score.should eq(0)

From a Demeter perspective, this seems to me indistinguishable from this example:

user.department.try(:name)

which according to Avdi Grimm is a violation of the Law of Demeter.

Source: http://devblog.avdi.org/2011/07/05/demeter-its-not-just-a-good-idea-its-the-law/

Answer 1

This is obviously subjective, but I believe it does not.

The should call is part of the language of RSpec, which just happens to be built upon Ruby. There’s no reason it couldn’t be:

should_be_equal(bowling.score, 0)

(or similar) but that’s not the language of RSpec. Further, the should method only exists on that object within specs, for the specs.

To try and (somewhat crudely, perhaps) better illustrate my argument about being a part of the language:

bowling.score + 10

is actually calling the + method on score, but would you see this as a law of demeter violation? The + is seen as an operator rather than a method, much like should be above.