Update tests

[fabaff]

The tests are not passing with later pytest releases. With pytest-5.0 there were some changes.

Executing pytestCheckPhase
============================= test session starts ==============================
platform linux -- Python 3.8.6, pytest-6.1.2, py-1.9.0, pluggy-0.13.1
rootdir: /build/source
plugins: vcr-1.0.2
collected 0 items / 1 error                                                    

==================================== ERRORS ====================================
______________________ ERROR collecting tests/test_vcr.py ______________________
tests/test_vcr.py:7: in <module>
    assert pytest.config.pluginmanager.hasplugin("vcr")
E   AttributeError: module 'pytest' has no attribute 'config'
=========================== short test summary info ============================
ERROR tests/test_vcr.py - AttributeError: module 'pytest' has no attribute 'c...
!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!