Android/Kotlin：如何检测作为参数传递的函数是否被调用

当然有办法解决这个问题啦！在Kotlin中测试这类作为高阶函数参数传入的lambda是否被执行，最便捷的方式是借助Mocking库（比如MockK，对Kotlin的函数类型支持特别到位），如果不想引入第三方库，也可以手动实现简单的调用追踪逻辑。下面针对你的场景给出具体方案：

方案一：使用MockK（推荐） #

MockK是专门为Kotlin设计的Mock库，能轻松追踪lambda的调用情况。

步骤1：添加MockK依赖 #

在你的项目构建文件（比如build.gradle.kts或build.gradle）中加入依赖：

// 针对JUnit 5
testImplementation("io.mockk:mockk:1.13.8")
testImplementation("org.junit.jupiter:junit-jupiter-api:5.9.2")
testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.9.2")

步骤2：编写测试用例 #

针对你的updateWeight函数，我们可以为每个传入的lambda创建mock，然后在调用目标方法后，验证对应的mock是否被调用：

import io.mockk.every
import io.mockk.mockk
import io.mockk.verify
import org.junit.jupiter.api.Test
import android.text.Editable
import android.text.SpannableStringBuilder

class WeightUpdateTest {

    @Test
    fun `当输入为空时，应调用showEmptyError`() {
        // 1. 创建各个lambda的mock
        val showEmptyErrorMock = mockk<() -> Unit>(relaxed = true)
        val showOutOfRangeErrorMock = mockk<() -> Unit>(relaxed = true)
        val dismissAlertDialogMock = mockk<() -> Unit>(relaxed = true)
        val updateAndShowMock = mockk<(Float) -> Unit>(relaxed = true)
        
        // 2. 创建空输入的Editable对象
        val emptyInput = SpannableStringBuilder("   ") // 带空格的空字符串，trim后为空

        // 3. 调用目标方法
        updateWeight(emptyInput, showEmptyErrorMock, showOutOfRangeErrorMock, dismissAlertDialogMock, updateAndShowMock)

        // 4. 验证只有showEmptyError被调用
        verify(exactly = 1) { showEmptyErrorMock() }
        verify(exactly = 0) { showOutOfRangeErrorMock() }
        verify(exactly = 0) { dismissAlertDialogMock() }
        verify(exactly = 0) { updateAndShowMock(any()) }
    }

    @Test
    fun `当输入超过300时，应调用showOutOfRangeError`() {
        val showEmptyErrorMock = mockk<() -> Unit>(relaxed = true)
        val showOutOfRangeErrorMock = mockk<() -> Unit>(relaxed = true)
        val dismissAlertDialogMock = mockk<() -> Unit>(relaxed = true)
        val updateAndShowMock = mockk<(Float) -> Unit>(relaxed = true)
        
        val overRangeInput = SpannableStringBuilder("350")

        updateWeight(overRangeInput, showEmptyErrorMock, showOutOfRangeErrorMock, dismissAlertDialogMock, updateAndShowMock)

        verify(exactly = 0) { showEmptyErrorMock() }
        verify(exactly = 1) { showOutOfRangeErrorMock() }
        verify(exactly = 0) { dismissAlertDialogMock() }
        verify(exactly = 0) { updateAndShowMock(any()) }
    }

    @Test
    fun `当输入在正常范围时，应调用dismissAlertDialog和updateAndShow`() {
        val showEmptyErrorMock = mockk<() -> Unit>(relaxed = true)
        val showOutOfRangeErrorMock = mockk<() -> Unit>(relaxed = true)
        val dismissAlertDialogMock = mockk<() -> Unit>(relaxed = true)
        val updateAndShowMock = mockk<(Float) -> Unit>(relaxed = true)
        
        val validInput = SpannableStringBuilder("75.5")
        val expectedValue = 75.5f

        updateWeight(validInput, showEmptyErrorMock, showOutOfRangeErrorMock, dismissAlertDialogMock, updateAndShowMock)

        verify(exactly = 0) { showEmptyErrorMock() }
        verify(exactly = 0) { showOutOfRangeErrorMock() }
        verify(exactly = 1) { dismissAlertDialogMock() }
        verify(exactly = 1) { updateAndShowMock(expectedValue) }
    }
}

这里的relaxed = true表示mock会自动返回默认值（对于无返回值的lambda来说就是什么都不做），避免我们手动设置每个mock的行为。

方案二：手动实现调用追踪（无需第三方库） #

如果不想引入MockK，你可以自己创建简单的类来记录函数是否被调用：

// 定义一个追踪类，用于记录函数调用状态
class CallTracker {
    var isCalled = false
        private set

    fun markCalled() {
        isCalled = true
    }
}

// 针对带参数的函数，可以扩展一个带参数记录的版本
class ParamCallTracker<T> {
    var lastCalledParam: T? = null
        private set
    var isCalled = false
        private set

    fun markCalled(param: T) {
        isCalled = true
        lastCalledParam = param
    }
}

然后编写测试用例：

import org.junit.jupiter.api.Test
import android.text.Editable
import android.text.SpannableStringBuilder
import kotlin.test.assertEquals
import kotlin.test.assertFalse
import kotlin.test.assertTrue

class WeightUpdateManualTest {

    @Test
    fun `空输入时触发showEmptyError`() {
        val emptyErrorTracker = CallTracker()
        val outOfRangeTracker = CallTracker()
        val dismissTracker = CallTracker()
        val updateTracker = ParamCallTracker<Float>()

        val emptyInput = SpannableStringBuilder("")

        updateWeight(
            value = emptyInput,
            showEmptyError = { emptyErrorTracker.markCalled() },
            showOutOfRangeError = { outOfRangeTracker.markCalled() },
            dismissAlertDialog = { dismissTracker.markCalled() },
            updateAndShow = { updateTracker.markCalled(it) }
        )

        assertTrue(emptyErrorTracker.isCalled)
        assertFalse(outOfRangeTracker.isCalled)
        assertFalse(dismissTracker.isCalled)
        assertFalse(updateTracker.isCalled)
    }

    @Test
    fun `正常输入时触发dismiss和updateAndShow`() {
        val emptyErrorTracker = CallTracker()
        val outOfRangeTracker = CallTracker()
        val dismissTracker = CallTracker()
        val updateTracker = ParamCallTracker<Float>()

        val validInput = SpannableStringBuilder("80")
        val expectedValue = 80f

        updateWeight(
            value = validInput,
            showEmptyError = { emptyErrorTracker.markCalled() },
            showOutOfRangeError = { outOfRangeTracker.markCalled() },
            dismissAlertDialog = { dismissTracker.markCalled() },
            updateAndShow = { updateTracker.markCalled(it) }
        )

        assertFalse(emptyErrorTracker.isCalled)
        assertFalse(outOfRangeTracker.isCalled)
        assertTrue(dismissTracker.isCalled)
        assertTrue(updateTracker.isCalled)
        assertEquals(expectedValue, updateTracker.lastCalledParam)
    }
}

这两种方案都能帮你精准验证不同输入场景下，哪个传入的函数会被执行。根据项目需求选择即可，MockK更适合复杂场景，手动追踪则更轻量。

内容的提问来源于stack exchange，提问作者kokilayaa