Being new to Ruby, one of the first things I wanted to do was figure out how to apply the testing style I am comfortable with in Java. Several years ago, Bob Lee and I wrote an IDEA plugin to generate stub-object source files from interface definitions. For a given interface:
The stub generator would create a class that looks like:
The generated stubs are useful in testing because I can set them up with a return value or exception to simulate some condition that I am trying to test. The methods of the stub keep track of whether they were called and any parameters that were passed to them. This approach follows the state-based testing that Fowler describes, and is central to my own programming style.
In Ruby, the same kind of thing can be accomplished at runtime in a very dynamic way. This unit test demonstrates the kind of thing I am looking for in a stub generator:
The Ruby Stub implementation was tricky to figure out until I learned how to use define_method:
So in my first real foray into a Ruby utility, I was able to create something that does what I need and learn a little about the API in the process. Of course, after savoring the feeling of learning and having written something that I thought was cool, I had a closer look the Stubba API from the Mocha library and realized that I still had a long way to go. Still, the exercise was a useful one; the more I use Ruby the more I really like it.
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