kotlin-testing

name	kotlin-testing
description	Kotlin 测试模式——Kotest、MockK、协程测试、基于属性的测试和 Kover 覆盖率。遵循 TDD 方法和惯用 Kotlin 实践。
origin	ECC

Kotlin 测试模式

使用 Kotest 和 MockK 遵循 TDD 方法编写可靠、可维护测试的综合 Kotlin 测试模式。

何时使用

• 编写新的 Kotlin 函数或类
• 为现有 Kotlin 代码添加测试覆盖
• 实现基于属性的测试
• 在 Kotlin 项目中遵循 TDD 工作流
• 配置 Kover 进行代码覆盖率

工作原理

1. 识别目标代码 — 找到要测试的函数、类或模块
2. 编写 Kotest 规范 — 选择匹配测试范围的规范风格（StringSpec、FunSpec、BehaviorSpec）
3. 模拟依赖 — 使用 MockK 隔离被测单元
4. 运行测试（RED） — 验证测试以预期错误失败
5. 实现代码（GREEN） — 编写最小代码使测试通过
6. 重构 — 在保持测试绿色的同时改进实现
7. 检查覆盖率 — 运行 ./gradlew koverHtmlReport 并验证 80%+ 覆盖率

示例

以下各节包含每种测试模式的详细、可运行示例：

快速参考

• Kotest 规范 — StringSpec、FunSpec、BehaviorSpec、DescribeSpec 示例见 Kotest 规范风格
• 模拟 — MockK 设置、协程模拟、参数捕获见 MockK
• TDD 演练 — 使用 EmailValidator 的完整 RED/GREEN/REFACTOR 周期见 Kotlin 的 TDD 工作流
• 覆盖率 — Kover 配置和命令见 Kover 覆盖率
• Ktor 测试 — testApplication 设置见 Ktor testApplication 测试

Kotlin 的 TDD 工作流

RED-GREEN-REFACTOR 循环

RED     -> 先写一个失败的测试
GREEN   -> 写最小代码使测试通过
REFACTOR -> 在保持测试绿色的同时改进代码
REPEAT  -> 继续下一个需求

Kotlin 中的 TDD 分步实践

// 步骤 1：定义接口/签名
// EmailValidator.kt
package com.example.validator

fun validateEmail(email: String): Result<String> {
    TODO("not implemented")
}

// 步骤 2：编写失败测试（RED）
// EmailValidatorTest.kt
package com.example.validator

import io.kotest.core.spec.style.StringSpec
import io.kotest.matchers.result.shouldBeFailure
import io.kotest.matchers.result.shouldBeSuccess

class EmailValidatorTest : StringSpec({
    "valid email returns success" {
        validateEmail("[e-mail]").shouldBeSuccess("[e-mail]")
    }

    "empty email returns failure" {
        validateEmail("").shouldBeFailure()
    }

    "email without @ returns failure" {
        validateEmail("userexample.com").shouldBeFailure()
    }
})

// 步骤 3：运行测试 - 验证失败
// $ ./gradlew test
// EmailValidatorTest > valid email returns success FAILED
//   kotlin.NotImplementedError: An operation is not implemented

// 步骤 4：实现最小代码（GREEN）
fun validateEmail(email: String): Result<String> {
    if (email.isBlank()) return Result.failure(IllegalArgumentException("Email cannot be blank"))
    if ('@' !in email) return Result.failure(IllegalArgumentException("Email must contain @"))
     regex = Regex()
     (!regex.matches(email))  Result.failure(IllegalArgumentException())
     Result.success(email)
}

Kotest 规范风格

StringSpec（最简单）

class CalculatorTest : StringSpec({
    "add two positive numbers" {
        Calculator.add(2, 3) shouldBe 5
    }

    "add negative numbers" {
        Calculator.add(-1, -2) shouldBe -3
    }

    "add zero" {
        Calculator.add(0, 5) shouldBe 5
    }
})

FunSpec（类 JUnit）

class UserServiceTest : FunSpec({
    val repository = mockk<UserRepository>()
    val service = UserService(repository)

    test("getUser returns user when found") {
        val expected = User(id = "1", name = "Alice")
        coEvery { repository.findById("1") } returns expected

        val result = service.getUser("1")

        result shouldBe expected
    }

    test("getUser throws when not found") {
        coEvery { repository.findById("999") } returns null

        shouldThrow<UserNotFoundException> {
            service.getUser("999")
        }
    }
})

BehaviorSpec（BDD 风格）

class OrderServiceTest : BehaviorSpec({
    val repository = mockk<OrderRepository>()
    val paymentService = mockk<PaymentService>()
    val service = OrderService(repository, paymentService)

    Given("a valid order request") {
        val request = CreateOrderRequest(
            userId = "user-1",
            items = listOf(OrderItem("product-1", quantity = 2)),
        )

        When("the order is placed") {
            coEvery { paymentService.charge(any()) } returns PaymentResult.Success
            coEvery { repository.save(any()) } answers { firstArg() }

            val result = service.placeOrder(request)

            Then("it should return a confirmed order") {
                result.status shouldBe OrderStatus.CONFIRMED
            }

            Then("it should charge payment") {
                coVerify(exactly = 1) { paymentService.charge(any()) }
            }
        }

        When("payment fails") {
            coEvery { paymentService.charge(any()) } returns PaymentResult.Declined

            Then("it should throw PaymentException") {
                shouldThrow<PaymentException> {
                    service.placeOrder(request)
                }
            }
        }
    }
})

DescribeSpec（RSpec 风格）

class UserValidatorTest : DescribeSpec({
    describe("validateUser") {
        val validator = UserValidator()

        context("with valid input") {
            it("accepts a normal user") {
                val user = CreateUserRequest("Alice", "[e-mail]")
                validator.validate(user).shouldBeValid()
            }
        }

        context("with invalid name") {
            it("rejects blank name") {
                val user = CreateUserRequest("", "[e-mail]")
                validator.validate(user).shouldBeInvalid()
            }

            it("rejects name exceeding max length") {
                val user = CreateUserRequest("A".repeat(256), "[e-mail]")
                validator.validate(user).shouldBeInvalid()
            }
        }
    }
})

Kotest 匹配器

核心匹配器

import io.kotest.matchers.shouldBe
import io.kotest.matchers.shouldNotBe
import io.kotest.matchers.string.*
import io.kotest.matchers.collections.*
import io.kotest.matchers.nulls.*

// 相等性
result shouldBe expected
result shouldNotBe unexpected

// 字符串
name shouldStartWith "Al"
name shouldEndWith "ice"
name shouldContain "lic"
name shouldMatch Regex("[A-Z][a-z]+")
name.shouldBeBlank()

// 集合
list shouldContain "item"
list shouldHaveSize 3
list.shouldBeSorted()
list.shouldContainAll("a", "b", "c")
list.shouldBeEmpty()

// 空值
result.shouldNotBeNull()
result.shouldBeNull()

// 类型
result.shouldBeInstanceOf<User>()

// 数字
count shouldBeGreaterThan 0
price shouldBeInRange 1.0..100.0

// 异常
shouldThrow<IllegalArgumentException> {
    validateAge(-1)
}.message shouldBe "Age must be positive"

shouldNotThrow<Exception> {
    validateAge(25)
}

自定义匹配器

fun beActiveUser() = object : Matcher<User> {
    override fun test(value: User) = MatcherResult(
        value.isActive && value.lastLogin != null,
        { "User ${value.id} should be active with a last login" },
        { "User ${value.id} should not be active" },
    )
}

// 用法
user should beActiveUser()

MockK

基本模拟

class UserServiceTest : FunSpec({
    val repository = mockk<UserRepository>()
    val logger = mockk<Logger>(relaxed = true) // 宽松模式：返回默认值
    val service = UserService(repository, logger)

    beforeTest {
        clearMocks(repository, logger)
    }

    test("findUser delegates to repository") {
        val expected = User(id = "1", name = "Alice")
        every { repository.findById("1") } returns expected

        val result = service.findUser("1")

        result shouldBe expected
        verify(exactly = 1) { repository.findById("1") }
    }

    test("findUser returns null for unknown id") {
        every { repository.findById(any()) } returns null

        val result = service.findUser("unknown")

        result.shouldBeNull()
    }
})

协程模拟

class AsyncUserServiceTest : FunSpec({
    val repository = mockk<UserRepository>()
    val service = UserService(repository)

    test("getUser suspending function") {
        coEvery { repository.findById("1") } returns User(id = "1", name = "Alice")

        val result = service.getUser("1")

        result.name shouldBe "Alice"
        coVerify { repository.findById("1") }
    }

    test("getUser with delay") {
        coEvery { repository.findById("1") } coAnswers {
            delay(100) // 模拟异步工作
            User(id = "1", name = "Alice")
        }

        val result = service.getUser("1")
        result.name shouldBe "Alice"
    }
})

参数捕获

test("save captures the user argument") {
    val slot = slot<User>()
    coEvery { repository.save(capture(slot)) } returns Unit

    service.createUser(CreateUserRequest("Alice", "[e-mail]"))

    slot.captured.name shouldBe "Alice"
    slot.captured.email shouldBe "[e-mail]"
    slot.captured.id.shouldNotBeNull()
}

Spy 和部分模拟

test("spy on real object") {
    val realService = UserService(repository)
    val spy = spyk(realService)

    every { spy.generateId() } returns "fixed-id"

    spy.createUser(request)

    verify { spy.generateId() } // 已覆盖
    // 其他方法使用真实实现
}

协程测试

使用 runTest 测试挂起函数

import kotlinx.coroutines.test.runTest

class CoroutineServiceTest : FunSpec({
    test("concurrent fetches complete together") {
        runTest {
            val service = DataService(testScope = this)

            val result = service.fetchAllData()

            result.users.shouldNotBeEmpty()
            result.products.shouldNotBeEmpty()
        }
    }

    test("timeout after delay") {
        runTest {
            val service = SlowService()

            shouldThrow<TimeoutCancellationException> {
                withTimeout(100) {
                    service.slowOperation() // 耗时 > 100ms
                }
            }
        }
    }
})

测试 Flow

import io.kotest.matchers.collections.shouldContainInOrder
import kotlinx.coroutines.flow.MutableSharedFlow
import kotlinx.coroutines.flow.toList
import kotlinx.coroutines.launch
import kotlinx.coroutines.test.advanceTimeBy
import kotlinx.coroutines.test.runTest

class FlowServiceTest : FunSpec({
    test("observeUsers emits updates") {
        runTest {
            val service = UserFlowService()

            val emissions = service.observeUsers()
                .take(3)
                .toList()

            emissions shouldHaveSize 3
            emissions.last().shouldNotBeEmpty()
        }
    }

    test("searchUsers debounces input") {
        runTest {
            val service = SearchService()
            val queries = MutableSharedFlow<String>()

            val results = mutableListOf<List<User>>()
            val job = launch {
                service.searchUsers(queries).collect { results.add(it) }
            }

            queries.emit("a")
            queries.emit("ab")
            queries.emit("abc") // 只有这个应该触发搜索
            advanceTimeBy(500)

            results shouldHaveSize 1
            job.cancel()
        }
    }
})

TestDispatcher

import kotlinx.coroutines.test.StandardTestDispatcher
import kotlinx.coroutines.test.advanceUntilIdle

class DispatcherTest : FunSpec({
    test("uses test dispatcher for controlled execution") {
        val dispatcher = StandardTestDispatcher()

        runTest(dispatcher) {
            var completed = false

            launch {
                delay(1000)
                completed = true
            }

            completed shouldBe false
            advanceTimeBy(1000)
            completed shouldBe true
        }
    }
})

基于属性的测试

Kotest 属性测试

import io.kotest.core.spec.style.FunSpec
import io.kotest.property.Arb
import io.kotest.property.arbitrary.*
import io.kotest.property.forAll
import io.kotest.property.checkAll
import kotlinx.serialization.json.Json
import kotlinx.serialization.encodeToString
import kotlinx.serialization.decodeFromString

// 注意：下面的序列化往返测试要求 User data class
// 使用 @Serializable 注解（来自 kotlinx.serialization）。

class PropertyTest : FunSpec({
    test("string reverse is involutory") {
        forAll<String> { s ->
            s.reversed().reversed() == s
        }
    }

    test("list sort is idempotent") {
        forAll(Arb.list(Arb.int())) { list ->
            list.sorted() == list.sorted().sorted()
        }
    }

    test("serialization roundtrip preserves data") {
        checkAll(Arb.bind(Arb.string(1..50), Arb.string(5..100)) { name, email ->
            User(name = name, email = "$[e-mail]")
        }) { user ->
            val json = Json.encodeToString(user)
            val decoded = Json.decodeFromString<User>(json)
            decoded shouldBe user
        }
    }
})

自定义生成器

val userArb: Arb<User> = Arb.bind(
    Arb.string(minSize = 1, maxSize = 50),
    Arb.email(),
    Arb.enum<Role>(),
) { name, email, role ->
    User(
        id = UserId(UUID.randomUUID().toString()),
        name = name,
        email = Email(email),
        role = role,
    )
}

val moneyArb: Arb<Money> = Arb.bind(
    Arb.long(1L..1_000_000L),
    Arb.enum<Currency>(),
) { amount, currency ->
    Money(amount, currency)
}

数据驱动测试

Kotest 中的 withData

class ParserTest : FunSpec({
    context("parsing valid dates") {
        withData(
            "2026-01-15" to LocalDate(2026, 1, 15),
            "2026-12-31" to LocalDate(2026, 12, 31),
            "2000-01-01" to LocalDate(2000, 1, 1),
        ) { (input, expected) ->
            parseDate(input) shouldBe expected
        }
    }

    context("rejecting invalid dates") {
        withData(
            nameFn = { "rejects '$it'" },
            "not-a-date",
            "2026-13-01",
            "2026-00-15",
            "",
        ) { input ->
            shouldThrow<DateParseException> {
                parseDate(input)
            }
        }
    }
})

测试生命周期和夹具

BeforeTest / AfterTest

class DatabaseTest : FunSpec({
    lateinit var db: Database

    beforeSpec {
        db = Database.connect("jdbc:h2:mem:test;DB_CLOSE_DELAY=-1")
        transaction(db) {
            SchemaUtils.create(UsersTable)
        }
    }

    afterSpec {
        transaction(db) {
            SchemaUtils.drop(UsersTable)
        }
    }

    beforeTest {
        transaction(db) {
            UsersTable.deleteAll()
        }
    }

    test("insert and retrieve user") {
        transaction(db) {
            UsersTable.insert {
                it[name] = "Alice"
                it[email] = "[e-mail]"
            }
        }

        val users = transaction(db) {
            UsersTable.selectAll().map { it[UsersTable.name] }
        }

        users shouldContain "Alice"
    }
})

Kotest 扩展

// 可复用的测试扩展
class DatabaseExtension : BeforeSpecListener, AfterSpecListener {
    lateinit var db: Database

    override suspend fun beforeSpec(spec: Spec) {
        db = Database.connect("jdbc:h2:mem:test;DB_CLOSE_DELAY=-1")
    }

    override suspend fun afterSpec(spec: Spec) {
        // 清理
    }
}

class UserRepositoryTest : FunSpec({
    val dbExt = DatabaseExtension()
    register(dbExt)

    test("save and find user") {
        val repo = UserRepository(dbExt.db)
        // ...
    }
})

Kover 覆盖率

Gradle 配置

// build.gradle.kts
plugins {
    id("org.jetbrains.kotlinx.kover") version "0.9.7"
}

kover {
    reports {
        total {
            html { onCheck = true }
            xml { onCheck = true }
        }
        filters {
            excludes {
                classes("*.generated.*", "*.config.*")
            }
        }
        verify {
            rule {
                minBound(80) // 覆盖率低于 80% 时构建失败
            }
        }
    }
}

覆盖率命令

# 运行测试并生成覆盖率
./gradlew koverHtmlReport

# 验证覆盖率阈值
./gradlew koverVerify

# 用于 CI 的 XML 报告
./gradlew koverXmlReport

# 查看 HTML 报告（使用适合你操作系统的命令）
# macOS:   open build/reports/kover/html/index.html
# Linux:   xdg-open build/reports/kover/html/index.html
# Windows: start build/reports/kover/html/index.html

覆盖率目标

代码类型	目标
关键业务逻辑	100%
公共 API	90%+
一般代码	80%+
生成/配置代码	排除

Ktor testApplication 测试

class ApiRoutesTest : FunSpec({
    test("GET /users returns list") {
        testApplication {
            application {
                configureRouting()
                configureSerialization()
            }

            val response = client.get("/users")

            response.status shouldBe HttpStatusCode.OK
            val users = response.body<List<UserResponse>>()
            users.shouldNotBeEmpty()
        }
    }

    test("POST /users creates user") {
        testApplication {
            application {
                configureRouting()
                configureSerialization()
            }

            val response = client.post("/users") {
                contentType(ContentType.Application.Json)
                setBody(CreateUserRequest("Alice", "[e-mail]"))
            }

            response.status shouldBe HttpStatusCode.Created
        }
    }
})

测试命令

# 运行所有测试
./gradlew test

# 运行特定测试类
./gradlew test --tests "com.example.UserServiceTest"

# 运行特定测试
./gradlew test --tests "com.example.UserServiceTest.getUser returns user when found"

# 详细输出运行
./gradlew test --info

# 带覆盖率运行
./gradlew koverHtmlReport

# 运行 detekt（静态分析）
./gradlew detekt

# 运行 ktlint（格式检查）
./gradlew ktlintCheck

# 持续测试
./gradlew test --continuous

最佳实践

应该做的：

• 首先编写测试（TDD）
• 在项目中一致使用 Kotest 的规范风格
• 对挂起函数使用 MockK 的 coEvery/coVerify
• 使用 runTest 进行协程测试
• 测试行为，而非实现
• 对纯函数使用基于属性的测试
• 使用 data class 测试夹具提高清晰度

不应该做的：

• 混合测试框架（选择 Kotest 并坚持使用）
• 模拟 data class（使用真实实例）
• 在协程测试中使用 Thread.sleep()（使用 advanceTimeBy）
• 跳过 TDD 中的 RED 阶段
• 直接测试私有函数
• 忽略不稳定的测试

与 CI/CD 集成

# GitHub Actions 示例
test:
  runs-on: ubuntu-latest
  steps:
    - uses: actions/checkout@v4
    - uses: actions/setup-java@v4
      with:
        distribution: 'temurin'
        java-version: '21'

    - name: Run tests with coverage
      run: ./gradlew test koverXmlReport

    - name: Verify coverage
      run: ./gradlew koverVerify

    - name: Upload coverage
      uses: codecov/codecov-action@v5
      with:
        files: build/reports/kover/report.xml
        token: ${{ secrets.CODECOV_TOKEN }}

记住：测试就是文档。它们展示 Kotlin 代码的预期使用方式。使用 Kotest 的表达性匹配器使测试可读，使用 MockK 进行整洁的依赖模拟。