mocking libaray for Kotlin Joe Tsai 2018.09.20 @ Android Taipei 

Joe Tsai Android Developer https://medium.com/joe-tsai 

Kotlin + Mockito 可能會遇到的問題 

嘗試 @mock Class org.mockito.exceptions.base.MockitoException: Cannot mock/spy class com.joetsai.kotlinunittest.token.TokenRepository Mockito cannot mock/spy because : - final class 

嘗試 @mock Class org.mockito.exceptions.base.MockitoException: Cannot mock/spy class com.joetsai.kotlinunittest.token.TokenRepository Mockito cannot mock/spy because : - final class → 在 Kotlin 中任何 Class 預設為 final 解法 1. Open class 2. 開啟隱藏版 mock final 功能 

其他可能遇到的問題 ● java.lang.IllegalStateException: anyObject() must not be null any(), eq(), capture(), captor() ● `when` 解法 1. MockitoKotlinHelpers.kt 2. Mockito-Kotlin 

測試 static 方法（PowerMock） ● 初始化繁瑣，使用上不直覺 ● “Mockito2 support is currently experimental. A lot of issues are not resolved still.” 版本兼容性 

只是想用 Kotlin 寫單元測試而已 有必要這麼折磨人嗎？ 

如果不用處理上述問題又可以測試靜態方法， 該有多好？ 

無痛在 Kotlin 下使用 Mockito + PowerMock 

Gradle Setting dependencies { testImplementation 'io.mockk:mockk:1.8.6' ... } 

Example: 小孩要零用錢 class Kid(private val mother: Mother) { var money = 0 private set fun wantMoney() { money += mother.giveMoney() } } class Mother { fun giveMoney(): Int { return 100 } } 

mockk, every class KidTest { @Test fun wantMoney() { // Given val mother = mockk() val kid = Kid(mother) every { mother.giveMoney() } returns 30 // when().thenReturn() in Mockito // When kid.wantMoney() // Then assertEquals(30, kid.money) } } 

Annotation class KidAnnotationTest { @MockK lateinit var mother: Mother lateinit var kid: Kid @Before fun setUp() { MockKAnnotations.init(this) kid = Kid(mother) } @Test fun wantMoney() { every { mother.giveMoney() } returns 30 kid.wantMoney() assertEquals(30, kid.money) } } 

需求變更：通知媽媽 class Kid(private val mother: Mother) { var money = 0 private set fun wantMoney() { mother.inform(money) money += mother.giveMoney() } } class Mother { fun inform(money: Int) { println("媽媽我現在有 $money 元，我要跟你拿錢！") } fun giveMoney(): Int { return 100 } } 

Verify @Test fun wantMoney() { // When val mother = mockk() val kid = Kid(mother) every { mother.giveMoney() } returns 30 // Given kid.wantMoney() // Then verify { mother.inform(any()) } assertEquals(30, kid.money) } 

Verify @Test fun wantMoney() { // When val mother = mockk() val kid = Kid(mother) every { mother.giveMoney() } returns 30 // Given kid.wantMoney() // Then verify { mother.inform(any()) } assertEquals(30, kid.money) } io.mockk.MockKException: no answer found for: Mother(#1).inform(0) 

Verify @Test fun wantMoney() { // When val mother = mockk() val kid = Kid(mother) every { mother.giveMoney() } returns 30 // Given kid.wantMoney() // Then verify { mother.inform(any()) } assertEquals(30, kid.money) } io.mockk.MockKException: no answer found for: Mother(#1).inform(0) 在 MockK 預設的 mock 是很嚴謹的，必須指定所 有的行為操作。 

Verify @Test fun wantMoney() { // When val mother = mockk() val kid = Kid(mother) every { mother.giveMoney() } returns 30 // Given kid.wantMoney() // Then verify { mother.inform(any()) } assertEquals(30, kid.money) } io.mockk.MockKException: no answer found for: Mother(#1).inform(0) 在 MockK 預設的 mock 是很嚴謹的，必須指定所 有的行為操作。 every { mother.inform(any()) } just Runs 

Relaxed Mocks 該物件所有的方法都不需要指定 // 第一種 val mother = mockk(relaxed = true) // 第二種 @RelaxedMockK lateinit var mother: Mother 

Relaxed Unit Function 不需指定無回傳值的方法 @MockK lateinit var mother: Mother @Before fun setUp() { MockKAnnotations.init(this, relaxUnitFun = true) } @MockK(relaxUnitFun = true) lateinit var mother: Mother 

Verify verify { mother.inform(any()) } verify(exactly = 0) { mother.inform(any()) } verify { mother.inform(any()) mother.giveMoney() } // inform() 的下一個執行的方法一定要是 giveMoney() verifySequence { mother.inform(any()) mother.giveMoney() } // inform() 只要在 giveMoney() 之前執行即可 verifyOrder { mother.inform(any()) mother.giveMoney() } 

Capture 用途：抓取方法參數 種類：slot, mutableListOf class Mother { fun inform(money: Int) { println("媽媽我現在有 $money 元，我要跟你拿錢！") } ... } val slot = slot() every { mother.inform(capture(slot)) } just Runs kid.wantMoney() assertEquals(0, slot.captured) 

Static Method class Util { fun ok() { UtilJava.ok() UtilKotlin.ok() } } object UtilKotlin { @JvmStatic fun ok(): String { return "UtilKotlin.ok()" } } public class UtilJava { static String ok() { return "UtilJava.ok()"; } } 

@Test fun ok() { // Given val util = Util() mockkStatic(UtilJava::class) mockkStatic(UtilKotlin::class) every { UtilJava.ok() } returns "Joe" every { UtilKotlin.ok() } returns "Tsai" // When util.ok() // Then verify { UtilJava.ok() } verify { UtilKotlin.ok() } assertEquals("Joe", UtilJava.ok()) assertEquals("Tsai", UtilKotlin.ok()) } MockkStatic 

Companion Object ? class Util { fun ok() { UtilKotlin.ok() } } class UtilKotlin { companion object { @JvmStatic fun ok(): String { return "UtilKotlin.ok()" } } } 

Test Companion Object @Test fun ok() { // Given val util = Util() mockkObject(UtilKotlin) mockkObject(UtilKotlin.Companion) every { UtilKotlin.ok() } returns "Tsai" // When util.ok() // Then verify { UtilKotlin.ok() } assertEquals("Tsai", UtilKotlin.ok()) } 兩個都能正常運作 

class Util { fun ok() { UtilKotlin.ok() } } Singleton object UtilKotlin { @JvmStatic fun ok(): String { return "UtilKotlin.ok()" } } 

MockkObject @Test fun ok() { // Given val util = Util() mockkObject(UtilKotlin) every { UtilKotlin.ok() } returns "Tsai" // When util.ok() // Then verify { UtilKotlin.ok() } assertEquals("Tsai", UtilKotlin.ok()) } 

What’s More ● Spy ● Extension functions ● Private functions ● Coroutines 

Reference ● MockK.io ● MOCKING IN KOTLIN WITH MOCKK ● Kotlin: Static Methods 

Let’s mockK