Recycling tests in TDD
The standard way that TDD is described is as Red-Green-Refactor:
Red: write a failing test
Green: get it to pass as quickly as possible
Refactor: improve the design, using the tests as a safety net
Repeat
TL;DR; I’ve found that step 1) might be better expressed as:
Red: write a failing test, or make an existing test fail
Print Diamond
One of the katas that I use in my TDD training is “Print Diamond”. The problem statement is quite simple:
Given a letter, print a diamond starting with ‘A’ with the supplied letter at the widest point.
For example: print-diamond ‘C’ prints
A
B B
C C
B B
A
I’ve used Cyber-Dojo to demonstrate two different approaches so you can follow along with my example, but I recommend you try this kata on your own before reading further. .
Gorilla
The usual approach is to start with a test for the simple case where the diamond consists of just a single ‘A’:
> PrintDiamond(‘A’)
A
The next test is usually for a proper diamond consisting of ‘A’ and ‘B’:
> PrintDiamond(‘B’)
A
B B
A
It’s easy enough to get this to pass by hardcoding the result. Then we move on to the letter ‘C’:
> PrintDiamond(‘C’)
A
B B
C C
B B
A
The code is now screaming for us to refactor it, but to keep all the tests passing most people try to solve the entire problem at once. That’s hard, because we’ll need to cope with multiple lines, varying indentation, and repeated characters with a varying number of spaces between them.
Moose
The approach that I’ve been playing with is to start as usual, with the simplest case:
> PrintDiamond(‘A’)
A
For the second test, however, we start by […]
