🧪 TEST: Make sure modules are truly modular

[mbercx]

In #264, @chrisjsewell rightly pointed out that participants should be able to just join any hands-on session even if they have fallen behind in previous once. So we have to make sure that the modules we are creating are indeed self-contained, i.e. that everything is there to run the content (without having to have installed the pseudos in a different section, for example).