Test*.test_mdrun failures under Python 3.x

[Oliver Beckstein]

The Gromacs 4.6.5 and 2018.2 tests with Python 3.6 fail (see #274), specifically

• TestAmber03star.test_mdrun
• TestAmber03w.test_mdrun
• TestCharmm22st.test_mdrun

(These tests already failed for PR #127 but we merged nevertheless. This issue addresses the required clean up.)

[Oliver Beckstein]

It is not yet clear if this is a bug in GromacsWrapper, something in the testing framework, or ... whatever.

Insights are very welcome!

[Oliver Beckstein]

This is almost certainly due to something in scaling.partial_tempering

GromacsWrapper/gromacs/scaling.py

Line 126 in 6b87aa8

 def partial_tempering(args):