Rspec: How to test recursion?

Question

I'd like to test that a method is called recursively with a specific argument.

My approach:

class Recursable
  def rec(arg)
    rec(7) unless arg == 7
  end
end

describe Recursable do
  it "should recurse" do
    r = Recursable.new('test')
    r.should_receive(:rec).with(0).ordered
    r.should_receive(:rec).with(7).ordered
    r.rec(0)
  end
end

Unexpectedly, RSpec fails with:

expected :rec with (7) once, but received it 0 times

Any idea what's wrong with my approach? How to test for effective recursion with a specific argument?

Answer 1

The problem with your test as it is now is that you are stubbing away the method you are trying to test. r.should_receive(:rec) is replacing r#rec with a stub, which of course doesn't ever call r.rec(7).

A better approach would be to simply test that the result of the initial method call is correct. It shouldn't strictly matter whether or not the method recurses, iterates, or phones a friend, as long as it gives the right answer in the end.