Backport PR #15763: Skip webagg test if tornado is not available.

tacaswell · meeseeksmachine · commit 9997e285492b · 2020-01-13T23:42:18.000Z
diff --git a/lib/matplotlib/tests/test_backend_webagg.py b/lib/matplotlib/tests/test_backend_webagg.py
@@ -6,6 +6,7 @@
 
 @pytest.mark.parametrize("backend", ["webagg", "nbagg"])
 def test_webagg_fallback(backend):
+    pytest.importorskip("tornado")
     if backend == "nbagg":
         pytest.importorskip("IPython")
     env = dict(os.environ)
