TST: verify warnings fail the test suite

Author: tacaswell

lib/matplotlib/tests/test_testing.py

@@ -0,0 +1,7 @@
+import warnings
+import pytest
+
+@pytest.mark.xfail(strict=True,
+                   reason="testing that warnings fail tests")
+def test_warn_to_fail():
+    warnings.warn("This should fail the test")