首先，对s3Client.putObject(..)的调用是您要测试的吗？发送到该方法的数据是否正确？
如果你把被测类和测试类分开会更容易一些，所以在主代码行中你应该有这样的内容：

import software.amazon.awssdk.core.sync.RequestBody
import software.amazon.awssdk.services.s3.S3Client
import software.amazon.awssdk.services.s3.model.PutObjectRequest

data class S3Object(
    val bucket: String,
    val key: String,
    val contents: String,
    val contentType: String,
)

class S3Service(
    // always in inject your dependencies then we can override then you override them in a test
    private val s3Client: S3Client = S3Client.create() 
) {
    fun putS3Object(s3Object: S3Object) {
        val putObjectRequest = PutObjectRequest.builder()
            .bucket(s3Object.bucket)
            .key(s3Object.key.toString())
            .contentType(s3Object.contentType)
            .build()
        s3Client.putObject(putObjectRequest, RequestBody.fromString(s3Object.contents))
    }
}

现在是测试类：

import io.kotest.matchers.shouldBe
import io.mockk.clearAllMocks
import io.mockk.every
import io.mockk.mockk
import io.mockk.slot
import org.junit.jupiter.api.BeforeEach
import org.junit.jupiter.api.Test
import software.amazon.awssdk.core.sync.RequestBody
import software.amazon.awssdk.services.s3.S3Client
import software.amazon.awssdk.services.s3.model.PutObjectRequest
import software.amazon.awssdk.services.s3.model.PutObjectResponse

class S3ServiceTest {

    // you need a mock the client since this is what you want to mock to check the invocation
    private val s3Client = mockk<S3Client>()
    private lateinit var s3Service: S3Service

    @BeforeEach
    fun beforeEach() {
        // its supposedly marginally more efficient to define your mocks once and clear then not instantiate each time
        clearAllMocks()
        // inject the mock s3Client so you do not get the `S3Client.create()` one
        s3Service = S3Service(s3Client)
    }

    @Test
    fun `putObject call correctly formed`() {
        val s3Object = S3Object(
            "test-bucket",
            "/test/key",
            "test-event",
            "application/json; charset=UTF-8",
        )
        every { s3Client.putObject(any<PutObjectRequest>(), any<RequestBody>()) } returns mockk()
        s3Service.putS3Object(s3Object)
    }

现在这是不完整的-它没有Assert任何东西。但这里的要点是，在every { s3Client.putObject(any<PutObjectRequest>(),...行中，我设置Mockk将捕获到putObject()的任何输入。在这种情况下，指示Mockk期望特定的输入是错误的......相反，您希望看到输入是什么，然后测试它（见下文）。
我需要使用<PutObjectRequest>，因为有几个s3Client.putObject()，所以mockk需要知道你在听哪个。
另一个变化是线的末端。你可以这样写：

} answers {putObjectResponse}

这是可以的，但有两件事
1.对于测试，您真的关心putObject()返回什么吗？如果这是更复杂测试的一部分，您可能会关心。如果不关心，请使用returns mock()
1.这里有两种“结尾”可以使用... returns OBJECT或answers { LAMBDA }。第二种情况在你不知道后面返回什么时很有用，在这种情况下你的输出是静态的，因为使用returns OBJECT更有效...
在需要正确返回的情况下，请执行以下操作：

val putObjectResponse = PutObjectResponse
            .builder()
            .build()
        every { s3Client.putObject(any<PutObjectRequest>(), any<RequestBody>()) } returns putObjectResponse

现在我们如何才能真正看到对putObject的调用是否正确呢？为此，您需要一个名为slot的不同特性，您可以这样使用：

@Test
    fun `putObject call correctly formed2`() {
        val s3Object = S3Object(
            "test-bucket",
            "/test/key",
            "test-event",
            "application/json; charset=UTF-8",
        )
        every { s3Client.putObject(any<PutObjectRequest>(), any<RequestBody>()) } returns mockk()

        val pubObjectRequestSlot = slot<PutObjectRequest>()
        every { s3Client.putObject(capture(pubObjectRequestSlot), any<RequestBody>()) } returns mockk()

        s3Service.putS3Object(s3Object)

        pubObjectRequestSlot.captured.bucket() shouldBe "test-bucket"
        pubObjectRequestSlot.captured.key() shouldBe "/test/key"
        // more assertions here...
        // and of course you can capture the RequestBody argument too
    }