SAPT tests are too slow

[ALescoulie]

SAPT Tests are too slow

Problem

At the moment the SAPT tests run a pair on 4AKE, the structure used in the MDAnalysis test files, and since it is running two amino acids are the dimer in SAPT it takes a large amount of time.

Possible Solution

We could make a very short trajectory of two helium atoms so that the SAPT calculation is faster while still ensure that core functionality is maintained. This would also reduce the size of our package by negating the need for a larger trajectory for tests.