Fix failing animation test with pytest 6.2.

anntzer · anntzer · commit 568afaf558fb · 2020-12-13T23:25:03.000+01:00
... per https://docs.pytest.org/en/stable/usage.html#unraisable.
diff --git a/lib/matplotlib/tests/test_animation.py b/lib/matplotlib/tests/test_animation.py
@@ -197,6 +197,8 @@ def test_animation_repr_html(writer, html, want, anim):
         html = anim._repr_html_()
     if want is None:
         assert html is None
+        with pytest.warns(UserWarning):
+            del anim  # Animtion was never run, so will warn on cleanup.
     else:
         assert want in html
 
