Revert back to testing with pytest in AppVeyor CI

Author: althonos

appveyor.yml

@@ -21,10 +21,11 @@ environment:
 install:
   # We need wheel installed to build wheels
   - "%PYTHON%\\python.exe -m pip install -U pip wheel setuptools"
+  - "%PYTHON%\\python.exe -m pip install pytest"
   - "%PYTHON%\\python.exe -m pip install -r tests/requirements.txt"
   - "%PYTHON%\\python.exe setup.py install"
 
 build: off
 
 test_script:
-  - "%PYTHON%\\python.exe -m unittest discover -vv"
+  - "%PYTHON%\\python.exe -m pytest"