cannot mock a method because there is when condition

How can I test this method isOpenOrClosed the when condition, i cannot mock it easily, because there is no method to test.I want to verify some condition for instance a status 2 and see that returns IamAnEnumWithTwoStatesOpenORCLoses.CLOSED

val statusType: ReturnASealedClass
        get() = when (statusIsAnIntFrom1To9FromTheApi) {

            1 -> ChildObject1
            2 -> ChildObject2
            3 -> ChildObject3
            4 -> ChildObject4
            5 -> ChildObject5
            6 -> ChildObject6
            7 -> ChildObject7
            8 -> ChildObject8
            9 -> ChildObject9

            else -> throw IllegalStateException("Status not supported")
        }


    val isOpenOrClosed
        get() = when (statusType) {

            ChildObject1,//All these Object inherit from FatherObject
         ChildObject2
    ChildObject3 -> IamAnEnumWithTwoStatesOpenORCLoses.CLOSED

            else -> IamAnEnumWithTwoStatesOpenORCLoses.OPEN
        }