Chessington
Chessington introduces test-driven development (TDD) to the learners, and has them iterating on an existing design to pass progressively more tricky tests.
KSBs
K7
software design approaches and patterns, to identify reusable solutions to commonly occurring problems
As in FizzBuzz, there will be patterns in use here. Make sure the trainer mentions them and encourages the learners to consider the situations that lead to their use.
K12
software testing frameworks and methodologies
TDD is a significant methodology for software development and testing, and the exercise introduces the learner to some language-specific testing frameworks.
S1
create logical and maintainable code
The trainer needs to encourage them to write it nicely. The more maintainable their code, the easier the learners will find adding the later features.
S4
test code and analyse results to correct errors found using unit testing
The main point of this exercise. Have the trainer explicitly teach the learners how to do this.
S7
apply structured techniques to problem solving, debug code and understand the structure of programmes in order to identify and resolve issues
This one is non-trivial: the trainer must teach the learners how to debug their code, and how to root through their code to figure out where the problem is and how to fix it.
S13
follow testing frameworks and methodologies
K12 above covers the knowledge of what methodology and frameworks that are introduced, and this KSB is the skill of applying that knowledge.