How to alter test object properties in KotlinTest via interceptTestCase

I am trying to use the interceptTestCase method to set up properties for a test case in KotlinTest as below:

class MyTest : ShouldSpec() {
    private val items = mutableListOf<String>()
    private var thing = 123

    override fun interceptTestCase(context: TestCaseContext, test: () -> Unit) {
        items.add("foo")
        thing = 456
        println("Before test ${items.size} and ${thing}")
        test()
        println("After test ${items.size} and ${thing}")
    }

    init {
        should("not work like this") {
            println("During test ${items.size} and ${thing}")
        }
    }
}

The output that I get is:

Before test 1 and 456

During test 0 and 123

After test 1 and 456

So the changes I have made are not visible within the test case. How should I change a property prior to each test being executed?