This line:
value = field.scheme.to_python(value)
raises an Exception when you upgrade to django 2.1. I don't know why it happens, but this workaround fixed the tests for me :).
Coverage decreased (-40.9%) to 40.86% when pulling 90bab2b3a24c071bdd81067f51d6a07b8661dab8 on ephes:patch-1 into 9e773265d5787fac2401f446b5a1acf827638b3d on klen:develop.
This line: value = field.scheme.to_python(value) raises an Exception when you upgrade to django 2.1. I don't know why it happens, but this workaround fixed the tests for me :).