ClassCastException when using Mockito.thenAnswer - kotlin

Question

I am new to Kotlin. I get exception when trying to use Mockito's thenAnswer method
Controller:
#RestController
class SampleRestController(
val sampleService: SampleService
) {
#PostMapping(value = ["/sample-endpoint"], consumes = [MediaType.APPLICATION_JSON_VALUE], produces = [MediaType.APPLICATION_JSON_VALUE])
fun sampleEndpoint(#RequestBody values: List<String>): ResponseEntity<String> {
val response = sampleService.serviceCall(values)
return ResponseEntity.status(HttpStatus.OK).body(response)
}
}
Service:
#Service
#Transactional
class SampleService {
fun serviceCall(values: List<String>): String {
return values.joinToString("")
}
}
Test:
#ExtendWith(MockitoExtension::class)
internal class SampleRestControllerTest {
#Mock
private lateinit var sampleService: SampleService
private lateinit var mockMvc: MockMvc
private lateinit var objectMapper: ObjectMapper
private lateinit var sampleRestController: SampleRestController
#BeforeEach
fun before() {
MockitoAnnotations.initMocks(this)
objectMapper = ObjectMapper()
.registerModule(JavaTimeModule())
.registerKotlinModule()
sampleRestController = SampleRestController(sampleService)
mockMvc = MockMvcBuilders.standaloneSetup(sampleRestController).build()
}
#Test
fun doTest() {
val testData = listOf("123", "456")
//Mockito.`when`(sampleService.serviceCall(testData)).thenReturn("123456")
//Mockito.`when`(sampleService.serviceCall(testData)).thenAnswer { invocation -> "123456" }
Mockito.`when`(sampleService.serviceCall(testData)).thenAnswer { invocation -> {
val numbers = invocation.getArgument<List<String>>(0)
if ("123" == numbers[0] && "456" == numbers[1]) {
"123456"
} else {
"654321"
}
} }
val result: MvcResult = mockMvc.perform(
MockMvcRequestBuilders.post("/sample-endpoint")
.content(objectMapper.writeValueAsString(testData))
.contentType(MediaType.APPLICATION_JSON_VALUE)
)
.andExpect(status().isOk)
.andReturn()
assertEquals("123456", result.response.contentAsString)
}
}
The unit test is working fine when using the thenReturn() and also when using thenAnswer() without any if condition.
When I try to use thenAnswer with if condition then I get classCastException.
Probably because Kotlin only accepts non-null value? How do I resolve this issue.

Answer 1

Check this.
#Test
fun doTest() {
val testData = listOf("123", "456")
//Mockito.`when`(sampleService.serviceCall(testData)).thenReturn("123456")
//Mockito.`when`(sampleService.serviceCall(testData)).thenAnswer { invocation -> "123456" }
Mockito.`when`(sampleService.serviceCall(testData)).thenAnswer(Answer<Any?> { invocationOnMock: InvocationOnMock ->
val values = invocationOnMock.getArgument<List<String>>(0)
if ("123" == values[0] && "456" == values[1]) {
return#Answer "123456"
}
return#Answer "654321"
})
val result: MvcResult = mockMvc.perform(
MockMvcRequestBuilders.post("/sample-endpoint")
.content(objectMapper.writeValueAsString(testData))
.contentType(MediaType.APPLICATION_JSON_VALUE)
)
.andExpect(status().isOk)
.andReturn()
assertEquals("123456", result.response.contentAsString)
}