add tests for make_config()

[annecori]

Currently only one small test added in #223

[annecori]

@thibautjombart @rebeccanash @sangeetabhatia03 any of us should be able to do this, pls comment below if you are going to tackle this so we know who is doing it

[sangeetabhatia03]

I can tackle it.

[sangeetabhatia03]

I have added tests and checked that they pass. If you or @rebeccanash can give me your thoughts on issue #242 I can then add one more test before I raise a PR.