Handle pytest's new ParameterSet for markers.

QuLogic · ArchangeGabriel · commit f4b430f0a59a · 2019-01-17T23:15:18.000+01:00
Using pytest.param(..., marks=pytest.mark.something) is a different type
than if using pytest.mark.something(...), so we need to handle that case
on skipping extensions.
diff --git a/lib/matplotlib/testing/decorators.py b/lib/matplotlib/testing/decorators.py
@@ -223,12 +223,18 @@ def _xfail_if_format_is_uncomparable(extension):
 
 def _mark_xfail_if_format_is_uncomparable(extension):
     if isinstance(extension, six.string_types):
-        will_fail = extension not in comparable_formats()
+        name = extension
+    elif isinstance(extension, tuple):
+        # Extension might be a pytest ParameterSet instead of a plain string.
+        # Unfortunately, this type is not exposed, so since it's a namedtuple,
+        # check for a tuple instead.
+        name = extension.values[0]
     else:
         # Extension might be a pytest marker instead of a plain string.
-        will_fail = extension.args[0] not in comparable_formats()
-    if will_fail:
-        fail_msg = 'Cannot compare %s files on this system' % extension
+        name = extension.args[0]
+
+    if name not in comparable_formats():
+        fail_msg = 'Cannot compare %s files on this system' % (name, )
         import pytest
         return pytest.mark.xfail(extension, reason=fail_msg, strict=False,
                                  raises=ImageComparisonFailure)
