Calling

/subsystem=undertow/configuration=handler/file=my-testing-handler:add(path="/some/path")

results in this failure description, which just prints the provided path.

{
    "outcome" => "failed",
    "failure-description" => "/some/path",
    "rolled-back" => true
}

The failure description should be enhanced to include information what it doesn't like about the path => e.g the path

doesn't exist on file system