SealedInterfaceTest.kt

package io.mockk.it

import io.mockk.every
import io.mockk.mockk
import org.junit.jupiter.api.condition.DisabledForJreRange
import org.junit.jupiter.api.condition.JRE
import kotlin.test.Test
import kotlin.test.assertEquals


class SealedInterfaceTest {

    @Test
    fun serviceReturnsSealedClassImpl() {
        val factory = mockk<Factory> {
            every { create() } returns Leaf(1)
        }

        val result = factory.create()

        assertEquals(Leaf(1), result)
    }

    @Test
    fun serviceAnswersSealedClassImpl() {
        val factory = mockk<Factory> {
            every { create() } answers { Leaf(1) }
        }

        val result = factory.create()

        assertEquals(Leaf(1), result)
    }

    @Test
    fun serviceTakesSealedInterfaceAsInput() {
        val formattedNode = "Formatted node"
        val factory = mockk<Factory> {
            every { format(any()) } answers { formattedNode }
        }

        val result = factory.format(Root(0))

        assertEquals(formattedNode, result)
    }

    companion object {

        sealed interface Node

        data class Root(val id: Int) : Node
        data class Leaf(val id: Int) : Node

        interface Factory {
            fun create(): Node

            fun format(node: Node): String
        }

        class FactoryImpl : Factory {
            override fun create(): Node = Root(0)

            override fun format(node: Node): String = node.toString()
        }

    }
}