TST: mark consistency tests as xfail

tests/test_file.py

@@ -211,6 +211,7 @@ def test_consistency_file_does_not_exist():
     assert c.messages["Info", 0][0] == "File system is consistent."
 
 
+@mark.xfail(reason="implementation is missins")
 def test_consistency_unknown_file():
     c = runCheck(None, None)
     assert c.messages["Info", 0] is not None