TST: Set xfail strict

[ci skip]

Author: pllim

setup.cfg

@@ -1,10 +1,11 @@
 [tool:pytest]
 testpaths = "astrowidgets" "docs"
 astropy_header = true
-# The comment below should be removed when the ginga problem with doctest
+# The commented lines below should be removed when the ginga problem with doctest
 # is fixed.
-# doctest_plus = disabled
-text_file_format = rst
+#doctest_plus = disabled
+#text_file_format = rst
+xfail_strict = true
 addopts = -p no:warnings
 
 [flake8]