Question

If I have a method that calls itself under a certain condition, is it possible to write a test to verify the behavior? I’d love to see an example, I don’t care about the mock framework or language. I’m using RhinoMocks in C# so I’m curious if it is a missing feature of the framework, or if I’m misunderstanding something fundamental, or if it is just an impossibility.

Answer 1

Assuming you want to do something like get the filename from a complete path, for example:

c:/windows/awesome/lol.cs -> lol.cs
c:/windows/awesome/yeah/lol.cs -> lol.cs
lol.cs -> lol.cs

and you have:

public getFilename(String original) {
  var stripped = original;
  while(hasSlashes(stripped)) {
    stripped = stripped.substringAfterFirstSlash(); 
  }
  return stripped;
}

and you want to write:

public getFilename(String original) {
  if(hasSlashes(original)) {
    return getFilename(original.substringAfterFirstSlash()); 
  }
  return original;
}

Recursion here is an implementation detail and should not be tested for. You really want to be able to switch between the two implementations and verify that they produce the same result: both produce lol.cs for the three examples above.

That being said, because you are recursing by name, rather than saying thisMethod.again() etc., in Ruby you can alias the original method to a new name, redefine the method with the old name, invoke the new name and check whether you end up in the newly defined method.

def blah
  puts "in blah"
  blah
end

alias blah2 blah

def blah
  puts "new blah"
end

blah2