The idea of TCR is that you work in very small increments and a little bit of test code and a little bit of production code. When you run the test if the test pass your changes are committed and if you tests fail your changes are reverted.
You can find the code created during this video in this GitHub repository.
In Episode 4 of Testing All The Things we continue to create the driving licence generator we started in the previous two videos. In this video we create a mock random number generator to create random digits to the end of the driving licence number.
You can find all the Test Double code in this GitHub repository or just the code created for the spy functionality in this commit