Bug report

Bug summary

During ArchLinux packaging builds, we have a bunch of errors related to 'MarkDecorator'.

Three different errors:

E TypeError: object of type 'MarkDecorator' has no len()
E AttributeError: 'MarkDecorator' object has no attribute 'encode'
E TypeError: cannot concatenate 'str' and 'MarkDecorator' objects

that lead to think it is supposed to be a string but actually is not.

Full log (minus irrelevant ImageComparisonFailure: images not close due to fonts/freetype2 differences) available here: https://paste.xinu.at/KRdO/

Likely yet another pytest issue?

Matplotlib version

• Operating system: ArchLinux
• Matplotlib version: 2.2.3 + Backport PRs #12154, #12294, #12297, #12316, #13159 & #13205 to fix multiple tests issues #13181 + 62297d1
• Python version: 2.7.15