Move whenCalledWith closer to expectBoundFunction

[tp]

Sounds good, let's do the change in a different PR though

Originally posted by @HenriBeck in https://github.com/tp/tsaga/diffs

[tp]

@HenriBeck I'd like to tackle this over the weekend to stay familiar with the code base.

[HenriBeck]

@tp any news on this? We will start with tsaga now and I would like to start using the ”final” testing implementation then to not introduce another change in a few weeks

[tp]

@HenriBeck Sorry, didn't get to it yet (who would've thought that 2 20 minute tasks are too much to take…). But I'll do it right now :)

[tp]

@HenriBeck Your approach of overlaying the interface on top of the implementation is very nice. Just have to shuffle a few interfaces instead of having to mess with lots of implementation code 🎉