String Calculator – Groovy

Itay Maman is a hopeless programmer living in Haifa (Israel). His doing a Ph.D. was just an excuse for writing cool software and for being able to read and hack cool code that others have written (Compilers and such).

I repeatedly practiced this Kata over the last few weeks. I eventually got to the point where I felt I’m doing it on “Auto pilot”. The Kata that I recorded was a bit different – I decided to take steps that are slightly than my usual, which made the whole thing interesting as I had to improvise here and there.

The nice thing about this Kata is its diversity. In “TDD By Example” Kent Beck lists three basic “moves”: (1) Fake it till you make it; (2) Triangulation; and (3) Obvious implementation. All three moves can be found here.

“Fake it” is my default. This quickly gets me to Green thereby providing the opportunity to refactor even before the implementation is complete. I like to think about it as a preemptive refactoring. You can see it in the last test. At 10:10 I inject a fake implementation. Then I do a preemptive refactoring: I introduce the “negs” variable which is the vehicle on which the real implementation is built.

Triangulation. 4:57 minutes into the Kata I am in a position where I reworked a “Fake it” implementation into a more general form, but I am not done. There is still a hard coded assignment: “delimiter = ‘;’”. At that point I felt that I covered enough grounds in the application code so I go back to the unit test and introduce a fresh test that fails (5:07). This leaves me with no option but to generalize the assignment into “delimiter = s.charAt(2).toString()”

Obvious implementation. There are three tests where the solution is just a few keystrokes away so I directly code it in. For example, when the shouldAllowNewlines() tests yields Red (3:38) I move to the application code, add a “|\\n” to the regular expression and get back to Green in 6 seconds.