Grails Unit test controller - unit-testing

Question

I'm trying to do a Unit test on this controller. I'm new to this sort of testing so I dont know from where do I start and how to test things that are needed to be tested, like user, render view.)
class ShoppingCartController {
def shoppingCartWebshopService
def shoppingCartService
def springSecurityService
def checkoutOperaService
def databaseService
def dodAdresaService
def payingOrder(SetShop1Command cmd) {
def user = springSecurityService.isLoggedIn() ? springSecurityService.currentUser.sifpartnera : null
def tempAdrese = databaseService.getAdrese(user)
def adrese = []
tempAdrese.each{
adrese.add(it.adresa)
}
if (cmd.hasErrors()) {
render(view: 'OrderChoseAddress', model: [cmd : cmd, params : params, adrese: adrese ])
}
def inputUnAdrese = params.inputUnAdrese
[inputUnAdrese: inputUnAdrese, adrese: adrese]
}
This is my test
#Mock([SpringSecurityService,DatabaseService])
#TestFor(ShoppingCartController)
class ShoppingCartControllerTests {
void testPayingOrder(){
when:
// params.user = 19
// user.equals(id)
// println user
// controller.OrderChoseAddress()
controller.params.user = "admin"
controller.databaseService = new DatabaseService()
then:
assert model.adrese != null
}