How to mock object creation inside a class in MockK using Kotlin?

Question

I have an aws lambda function as below:

    class FooHandler: RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
    
        private val lambdaClient = LambdaClient.create()
        private val logger = LogManager.getLogger(CollectorHandler::class)
    
        override fun handleRequest(request: APIGatewayProxyRequestEvent, context: Context): APIGatewayProxyResponseEvent {
    
            val response = APIGatewayProxyResponseEvent()
    
            if (isRequiredHeaderEmpty(request, response) || isBodyEmpty(request, response)) {
                return response
            }
return response

I am writing a unit test for aws lambda using MockK. Following is the test class:

class FooHandlerTest {

    private val request = APIGatewayProxyRequestEvent()
    private var response = APIGatewayProxyResponseEvent()
    @SpyK
    private lateinit var handler: FooHandler
    @MockK
    private lateinit var lambdaClient: LambdaClient
    @MockK
    private lateinit var context: Context

    @BeforeTest
    fun setUp() {

        handler = spyk()
        lambdaClient = mockk()
        context = mockk()
    }


    @Test
    fun testHandleRequestWhenBodyIsEmpty(){

        request.body=""
        response = handler.handleRequest(request, context)
        expectThat(response.statusCode).isEqualTo(HttpStatus.BAD_REQUEST)

    }

When I run the test I get the following error:

io.mockk.MockKException: Can't instantiate proxy via default constructor for class FooHandler

When I looked further it also gave this error: Caused by: software.amazon.awssdk.core.exception.SdkClientException: Unable to load region from any of the providers in the chain software.amazon.awssdk.regions.providers.DefaultAwsRegionProviderChain@7668d560

It looks like it is not mocking LambdaClient and is calling the actual function. Any ideas how can I reliably test my handler function.

I am not sure what you seek to do is even possible. Can you clarify - are you trying to test `FooHandler` but mocking `LambdaClient`? — AndrewL, Mar 01 '23 at 17:00

score 0 · Answer 1 · answered Mar 05 '23 at 17:22

I was able to resolve it. I am using strikt for assertions and mockK for mocking in kotlin:

class FooHandlerTest {

    private val request = APIGatewayProxyRequestEvent()
    private var response = APIGatewayProxyResponseEvent()
    @SpyK
    private lateinit var handler: FooHandler
    @MockK
    private lateinit var lambdaClient: LambdaClient
    @MockK
    private lateinit var context: Context

    @BeforeTest
    fun setUp(){

        mockkStatic(LambdaClient::class)
        context = mockk()
        lambdaClient = mockk()
        every { LambdaClient.create()} returns lambdaClient
        handler = spyk()

    }

How to mock object creation inside a class in MockK using Kotlin?

1 Answers1