Should validphys tests use new API

Created by: wilsonmr

recently I have been changing some of the underlying functionality of certain functions, see for example #427

Each time all of the tests have to be changed because they're using providers explicitly, until this is done the build breaks, see #447

One of the advantages with the API would be that we can rewrite these tests to use runcard level inputs, so that the backend can easily be completely changed, provided the end result is the same.

I'm not sure exactly which tests would want to rely solely on the API, because I guess if each test made a new call to the API the intermediate results wouldn't be cached in the same way that they currently are with the tests, which would lead to a slow down.