Revert "Revert "Enable building in parallel with pytest-xdist""

This reverts commit 21d68bd.

Author: DRMacIver

scripts/basic-test.sh

@@ -16,9 +16,9 @@ for k, v in sorted(dict(os.environ).items()):
 '
 
 if [ "$(python -c 'import sys; print(sys.version_info[:2] >= (3, 5))')" = "True" ] ; then
-  PYTEST="python -m pytest --assert=plain"
+  PYTEST="python -m pytest --assert=plain -n 2"
 else
-  PYTEST="python -m pytest"
+  PYTEST="python -m pytest -n 2"
 fi
 
 $PYTEST tests/cover

tox.ini

@@ -7,6 +7,7 @@ passenv=HOME
 [testenv]
 deps =
     pytest
+    pytest-xdist
 whitelist_externals=
   bash
 setenv=