Wrapping Mockito Mocks for Reusability

a_Classes.kt

/** Whether the Oven command was successful, or something happened */
sealed class OvenResult {
    object Success : OvenResult()
    data class Failure(val e: Exception) : OvenResult()
}

/** Class we will use Mockito to Mock */
class Oven {
    fun setTemperatureFahrenheit(tempF: Int) {
        TODO("Implementation Goes Here")
    }

    fun setTimeMinutes(minutes: Int) {
        TODO("Implementation Goes Here")
    }

    fun start(): OvenResult {
        TODO("Implementation Goes Here")
    }
}

/** Class that uses [Oven] */
class Dessert(val oven: Oven) {
    fun bakeCake(): OvenResult {
        oven.setTemperatureFahrenheit(350)
        oven.setTimeMinutes(30)
        return oven.start()
    }
}

b_OriginalTests.kt

import com.nhaarman.mockitokotlin2.mock
import com.nhaarman.mockitokotlin2.verify
import com.nhaarman.mockitokotlin2.whenever
import org.junit.Test

/** Test Dessert Baking */
class DessertTest {

    @Test
    fun bakeCakeSuccess() {
        val oven: Oven = mock()
        val dessert = Dessert(oven)

        // Mock Setup
        whenever(oven.start()).thenReturn(OvenResult.Success)

        // Execute Code
        dessert.bakeCake()

        // Verification
        verify(oven).setTemperatureFahrenheit(350)
        verify(oven).setTimeMinutes(30)
    }
}

c_FakeOven.kt

/** Wraps the Mockito mock for reuse */
class FakeOven {

    val mock: Oven = mock()

    fun givenOvenResult(ovenResult: OvenResult) {
        // Mock Setup
        whenever(mock.start()).thenReturn(ovenResult)
    }

    fun thenOvenSetTo(temperatureFahrenheit: Int, timeMinutes: Int) {
        // Verification
        verify(mock).setTemperatureFahrenheit(temperatureFahrenheit)
        verify(mock).setTimeMinutes(timeMinutes)
    }
}

d_UpdatedTests.kt

class DessertTestWithFake {

    @Test
    fun bakeCakeSuccess() {
        val fakeOven = FakeOven()
        val dessert = Dessert(fakeOven.mock)

        fakeOven.givenOvenResult(OvenResult.Success)
        dessert.bakeCake()
        fakeOven.thenOvenSetTo(
            temperatureFahrenheit = 350,
            timeMinutes = 30
        )
    }
}

e_LotsOfTests.kt

class DessertTestsWithFake {

    @Test
    fun bakeCake() {
        val fakeOven = FakeOven()
        val dessert = Dessert(fakeOven.mock)

        fakeOven.givenOvenResult(OvenResult.Success)
        dessert.bakeCake()
        fakeOven.thenOvenSetTo(
            temperatureFahrenheit = 350,
            timeMinutes = 30
        )
    }
  
  @Test
    fun bakeCupcakes() {
        val fakeOven = FakeOven()
        val dessert = Dessert(fakeOven.mock)

        fakeOven.givenOvenResult(OvenResult.Success)
        dessert.bakeCupcakes()
        fakeOven.thenOvenSetTo(
            temperatureFahrenheit = 350,
            timeMinutes = 20
        )
    }
  
  
    @Test
    fun bakeCookie() {
        val fakeOven = FakeOven()
        val dessert = Dessert(fakeOven.mock)

        fakeOven.givenOvenResult(OvenResult.Success)
        dessert.bakeCupcakes()
        fakeOven.thenOvenSetTo(
            temperatureFahrenheit = 375,
            timeMinutes = 16
        )
    }
}