Others have answered but interestingly, TDD was 'built-in' to the Pharo tutorial I did a while back. Basically you write a test first, say it calls an undefine

Others have answered but interestingly, TDD was 'built-in' to the Pharo tutorial I did a while back. Basically you write a test first, say it calls an undefined method `x.somemethod()`. You push a button to run the test, as soon as the method call fails, the environment shows you a popup which lets you define the method right then and there, while you have all the details of the suspended execution. You can write the method and the 'resume' the execution from where it excepted.