Add test to ensure correct sphinx versions are being used.

Author: domdfcoding

tests/test_sphinx_version.py

@@ -0,0 +1,13 @@
+# stdlib
+import os
+import re
+
+# 3rd party
+import sphinx
+
+
+def test_sphinx_version_against_tox():
+	m = re.match(r"py.*-sphinx(\d)\.(\d)", os.getenv("TOX_ENV_NAME", ''))
+	if m is not None:
+		target_version = tuple(map(int, m.groups()))
+		assert target_version == sphinx.version_info[:2]