I've just uploaded my second ever Youtube video! I've been procrastinating on this for over a month, but this is a video of me tackling the Mars Rover Kata in Typescript. Most versions of this I've seen use an outside-in style, but instead I'm using a bottom-up approach. I'd love feedback, on Youtube or Twitter. If people are interested, I've got two more parts to edit and upload.

Approval testing is a powerful technique for working with legacy systems. When refactoring, it's important that we have tests to tell us if we've changed behaviour, but sometimes code can be smelly enough that writing unit tests is hard. Approval tests fill this gap. Instead of writing behavioural unit tests, we capture the output of the system - usually as text - and run a diff tool to check for changes in the output as we change the code.

I've previously struggled to set up approval tests with the common tools and libraries, but I realised today that Jest Snapshots solve exactly the same problem, and are easy to use.

While spelunking through some code at work, I found a neat little programming problem that I've cleaned up a little and decided to publish as a TDD Kata.

In the Cake Shop Kata we're asked to write some code that can calculate the delivery date for different types of cakes, taking into account the skills and working patterns of the bakers.

I spend a lot of time teaching TDD to engineers. Some of my most rewarding sessions are spent with first-time TDD practitioners. When we're starting out, I'll choose a simple TDD kata, and we'll pair to solve it together.

Once I've introduced myself and the exercise, I always ask the same opening question: "What's the first test we should write?"

The answers are always interesting, because they tell me how the candidate thinks about TDD. If they have misconceptions, it's best to tackle them at the beginning. In my experience there are three common ways that people go wrong when choosing the first test.