Controller

    def save = {
        def project = new Project(params)
        if(!project.hasErrors() && project.save(flush:true)) {
            redirect(action:'edit',id:project.id)
        } else {
            render(view:'create',model:[project:project])
        }
    }

Controller Test

protected void setUp() {
        super.setUp()
        mockDomain(Project,[])
        mockDomain(Client,[])
}

public void testSaveNewProjectRedirect(){
	controller.params.name = "project one"
	controller.params.description = "a project to test"
	controller.params.id = 1

        controller.save()
	assertEquals "edit", controller.redirectArgs.action
}

Test Result

controller.redirectArgs is null??!?!?!?!

controller.save() returns null