Make sure code generated by Boilerplate are tested

[kailuowang]

Right now a good portion of which is not. E.g. SemigroupArityFunctions and ApplyArityFunctions

I believe this issue replicates #383, with the possible difference that #383 is specifically for auto generating the tests.

Perhaps best to clarify here and close #383 ?

[ceedubs]

Closing as a duplicate of #383.