Why does the second test faile?

TestTest.kt

import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.TestInstance

/** Test that tests run and that particular testing techniques work. */
@TestInstance(TestInstance.Lifecycle.PER_CLASS)
class KtTestTest {

    var state = "initial"

    @Test
    fun `first test sees original state`() {
        println("this: ${this}")
        println("state: ${state}")
        assertEquals("initial", state)
        state = "modified"
    }

    @Test
    fun `state changed by first test`() {
        println("this: ${this}")
        println("state: ${state}")
        assertEquals("modified", state)
        state = "modified again"
    }

}

"""
Output:

this: KtTestTest@7113b13f
state: initial

org.opentest4j.AssertionFailedError: 
Expected :modified
Actual   :initial

this: KtTestTest@7113b13f
state: initial
"""