How can I test the session variables in Grails?

I have two issues with testing a Grails controller.

I have a controller contains some methods like this one:

def save() {
    def x =session.SPRING_SECURITY_CONTEXT.authentication.principal.id
    def user = User.get(x)
}

and to test this I wrote the test method like this:

def testSave () {
    myCont.save()
}

And when I run this, I see a WARN from the database while getting the user which is:

[main] WARN core.DatastoreUtils - Cannot unbind session, there's no SessionHolder registered

So, my questions are:

• How to inject or init the session while testing so I can get this user from session?
• How can I remove the WARN message?