tests/conftest.py: tox: Remove root dir from sys.path

When using tox, it can accidentally pick up a {pymssql,_mssql}.so file
in the root directory and then get ImportError because of
incompatibility in Python versions. By removing the root directory from
the sys.path, it forces tox to import the library from correct place in
the tox virtualenv.

Author: msabramo

tests/conftest.py

@@ -1,3 +1,14 @@
+from os.path import dirname
+import sys
+
+# When using tox, it can accidentally pick up a {pymssql,_mssql}.so file in the
+# root directory and then get ImportError because of incompatibility in Python
+# versions. By removing the root directory from the sys.path, it forces tox to
+# import the library from correct place in the tox virtualenv.
+if '.tox' in sys.executable:
+    root_dir = dirname(dirname(__file__))
+    sys.path.remove(root_dir)
+
 import decimal
 import os
 try: