Thanks 
I’d seen the P5 TDD article and had a read through it. I’m not a TDD expert but I think mocks are more for when you want to create a fake version of the function being called so that you can see how many times it has been called by the function you are unit testing for example.
If not I’ll see if using mocha/chaj might work easier with p5. It should be possible to use any testing framework but we’ll see!
I’l have a read through tomorrow and see if I can work it out.