New tests for ".N" target mappings

[warrenmcg]

Hi @pimentel,

I've put together some quick tests to make sure that sleuth_prep only provides a warning if ".N" target_ids are provided with the Kallisto results, but not with the target mappings.

Note that this depends on incorporating the code from my previous pull request, since it runs the one sample from small_test_data, and otherwise the code will throw an error when run.

Note also that there is an error if the opposite occurs (Kallisto results do not have ".N", but the target mappings do), but I presume this case isn't accounted for because it's an unusual edge case?

[pimentel]

as usual, thanks a bunch!

indeed, I would rather the user remove the ".N" from the target_id in the target_mapping manually so that they are aware of the issue. and also this is not typical. when the issue is in the kallisto annotation then it is harder to deal with and quite difficult within the sleuth framework which is why we test for it.