Depending on what seems to have been timing conditions,...

Depending on what seems to have been timing conditions, connectNodeShouldSucceedWithForce could fail with a cryptic message.
Found an error in the launch log:
java.lang.IllegalStateException: Already connected
	at hudson.slaves.SlaveComputer.setChannel(SlaveComputer.java:567)
	at hudson.slaves.SlaveComputer.setChannel(SlaveComputer.java:390)
	at hudson.slaves.CommandLauncher.launch(CommandLauncher.java:132)
	at hudson.slaves.SlaveComputer$1.call(SlaveComputer.java:262)
I think the slave was being launched in the background, and then the test tried to disconnect and reconnect it.
Perhaps if these actions overlapped in time, the loose locking semantics of SlaveComputer.setChannel could cause the error.