> pip install -e .[test]
...
ERROR: pip's legacy dependency resolver does not consider dependency conflicts when selecting packages. This behaviour is the source of the following dependency conflicts.
pytest-cov 2.10.1 requires pytest>=4.6, but you'll have pytest 3.10.1 which is incompatible.
pytest-xdist 1.34.0 requires pytest>=4.4.0, but you'll have pytest 3.10.1 which is incompatible.
Requirement to pytest needs to be updated to v4