掌握 Kotlin Android 单元测试：MockK 框架深度实践指南

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掌握 Kotlin Android 单元测试：MockK 框架深度实践指南

在 Android 开发中，单元测试是保障代码质量的核心手段。但面对复杂的依赖关系和 Kotlin 语言特性，传统 Mock 框架常显得力不从心。本文将带你深入 MockK —— 一款专为 Kotlin 设计的 Mock 框架，通过 真实场景代码示例，助你彻底掌握 MockK 的精髓。

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一、为什么选择 MockK？

1.1 Kotlin 原生支持优势

• 协程友好：直接 Mock 挂起函数（coEvery/coVerify）
• 对象声明处理：轻松 Mock object 单例类
• 扩展函数支持：无需特殊配置即可模拟扩展方法
• DSL 语法糖：代码简洁程度提升 50%

1.2 性能对比

框架	启动时间	内存占用	Kotlin 适配度
MockK	120ms	45MB	★★★★★
Mockito	200ms	60MB	★★★☆☆
PowerMock	350ms	85MB	★★☆☆☆

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二、快速配置（Gradle）

// module/build.gradle.kts
dependencies {testImplementation("io.mockk:mockk:1.13.8")testImplementation("io.mockk:mockk-agent-jvm:1.13.8") // 解决 JDK 17+ 兼容问题androidTestImplementation("io.mockk:mockk-android:1.13.8") // 仪器化测试testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.7.3") // 协程支持
}

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三、核心功能全解析

3.1 基础 Mock 操作

场景 1：简单方法模拟

interface AuthService {fun login(username: String, password: String): Boolean
}@Test
fun `login should return true when credentials valid`() {val authMock = mockk<AuthService>()// Stubbing 配置every { authMock.login(username = eq("admin"), // 精确匹配password = any()        // 任意密码) } returns trueassertTrue(authMock.login("admin", "123456"))verify(exactly = 1) { authMock.login(any(), any()) }
}

场景 2：异常抛出模拟

class PaymentProcessor {fun process(amount: Double) {if (amount <= 0) throw IllegalArgumentException()// 真实支付逻辑}
}@Test
fun `process should throw when amount invalid`() {val processor = mockk<PaymentProcessor>()every { processor.process(any()) } throws IllegalArgumentException("Invalid amount")assertThrows<IllegalArgumentException> {processor.process(-100.0)}
}

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3.2 参数高级操作

场景 3：参数捕获与验证

class AnalyticsTracker {fun trackEvent(event: String, params: Map<String, Any>) {// 上报事件}
}@Test
fun `trackEvent should contain purchase event`() {val tracker = mockk<AnalyticsTracker>()val eventSlot = slot<String>()val paramsSlot = slot<Map<String, Any>>()every { tracker.trackEvent(capture(eventSlot),capture(paramsSlot)) } just Runs // 表示无需返回值tracker.trackEvent("purchase", mapOf("amount" to 99.9))assertEquals("purchase", eventSlot.captured)assertEquals(99.9, paramsSlot.captured["amount"])
}

场景 4：灵活参数匹配

class UserValidator {fun isEligible(user: User): Boolean {// 复杂验证逻辑return user.age >= 18 && !user.isBanned}
}@Test
fun `user should be eligible when meets conditions`() {val validator = mockk<UserValidator>()// 使用匹配器组合every { validator.isEligible(match { user -> user.age >= 18 && user.name.startsWith("A")}) } returns trueval testUser = User(name = "Alice", age = 20)assertTrue(validator.isEligible(testUser))
}

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四、高级技巧实战

4.1 静态方法与单例 Mock

场景 5：单例对象 Mock

object NetworkConfig {fun getBaseUrl() = "https://production.api"
}@Test
fun `mock singleton object`() {mockkObject(NetworkConfig)every { NetworkConfig.getBaseUrl() } returns "https://test.api"assertEquals("https://test.api", NetworkConfig.getBaseUrl())unmockkObject(NetworkConfig) // 清理
}

场景 6：静态工具类 Mock

class StringUtils {companion object {fun capitalize(str: String) = str.capitalize()}
}@Test
fun `mock static method`() {mockkStatic(StringUtils.Companion::class)every { StringUtils.capitalize(any()) } returns "MOCKED"assertEquals("MOCKED", StringUtils.capitalize("hello"))
}

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4.2 协程与挂起函数

场景 7：ViewModel 测试

class ProductViewModel(private val repo: ProductRepository
) : ViewModel() {private val _products = MutableStateFlow<List<Product>>(emptyList())val products = _products.asStateFlow()fun loadProducts() {viewModelScope.launch {_products.value = repo.fetchProducts()}}
}@Test
fun `loadProducts should update state`() = runTest {val repo = mockk<ProductRepository>()val testProducts = listOf(Product("Mocked Phone"))coEvery { repo.fetchProducts() } returns testProductsval viewModel = ProductViewModel(repo)viewModel.loadProducts()// 使用 Turbine 库简化 Flow 测试viewModel.products.test {assertEquals(emptyList(), awaitItem()) // 初始状态assertEquals(testProducts, awaitItem())cancel()}
}

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4.3 Android 平台特殊处理

场景 8：Context 模拟

class StringProvider(private val context: Context) {fun getAppName() = context.getString(R.string.app_name)
}@Test
fun `mock context resources`() {val mockContext = mockk<Context>()val mockRes = mockk<Resources>()every { mockContext.resources } returns mockResevery { mockRes.getString(R.string.app_name) } returns "MockApp"val provider = StringProvider(mockContext)assertEquals("MockApp", provider.getAppName())
}

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五、最佳实践清单

1. 分层验证策略：

   verify {service.callMethod(exact = 1) // 精确次数service.anotherMethod(atLeast = 2) // 最少调用
   }
   

2. 组合验证：

   verifyAll {service.methodA()service.methodB()
   }
   

3. 智能参数捕获：

   val allParams = mutableListOf<String>()
   every { service.log(capture(allParams)) } just Runs
   

4. 真实对象部分模拟：

   val realService = RealService()
   val spy = spyk(realService)every { spy.shouldMock() } returns false
   

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六、常见陷阱规避

陷阱 1：未清理 Mock 状态

@After
fun tearDown() {unmockkAll() // 必须清理防止测试污染
}

陷阱 2：错误的作用域验证

class OrderService {private fun internalValidate() { /* ... */ } // 私有方法无法 Mock
}// 正确做法：重构为 protected 或使用接口

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结语

建议在实际项目中：

1. 从简单场景入手，逐步尝试高级功能
2. 结合 Kotlin 协程测试工具（如 runTest）
3. 定期查看 MockK 官方文档 获取更新