func XFail(reason string, f func(), condition ...bool)
XFail replaces the default Fail handler with a XFail for one occurrence.
XFail skips the test once it fails and leaves a XFAIL label on the message.
It is useful to mark tests as XFail when one wants them to run even though they fail,
monitoring and collecting information.
'condition' can be used to specify whether the test should be marked as XFail