Specify the minimum required version of pytest
A previous change introduced the usage of pytest.param to our test suite in commit 7aba0bfc.
This was only added to pytest 3.1.0, and the tests can't work with older versions.
A previous change introduced the usage of pytest.param to our test suite in commit 7aba0bfc.
This was only added to pytest 3.1.0, and the tests can't work with older versions.