fun test() {
    SamTest.test(Foo<String, Int> { (s, n) -> "" })
    SamTest.test(Foo { (s: MutableList<X<Int>>, n: X<MutableSet<String>>) -> "" })
    SamTest.test(Foo { (s: MutableList<X<Int>>, n: X<MutableSet<String>>): X<MutableList<String>>? -> "" })
}