NotificationServiceTest.kt

class NotificationServiceTest : Spek({
    describe(".notify") {
        context("when message creation fails") {
            // constants
            val messagingServiceId = "message-service-id"
            val errorCode = 9
            val errorMessage = "error message"
            
            
            val restClient = mock<TwilioRestClient>()
            val secretRepository = mock<SecretRepository> {
                on { getTwilloMessagingServiceId() } doReturn messagingServiceId
            }

            val notificationService = NotificationService(restClient, secretRepository)
            val notificationRequest = NotificationRequest("+66", "839992233", "text")

            // We create a creator that returns a mocked `MessageCreator`
            // and now we can determine to behavior of function `create`
            fun creator(phoneNumber: PhoneNumber, messagingServiceId: String, text: String): MessageCreator =
                    mock {
                        on { create(restClient) } doReturn Message.fromJson(
                            """
                                {
                                  "error_code": $errorCode,
                                  "error_message": "$errorMessage",
                                  "status": "failed"
                                }
                            """.trimIndent(), jacksonObjectMapper())
                    }

            // notice that I use `::creator` to refer to `creator` as a value that can be passed
            val result = notificationService.notify(notificationRequest, ::creator)

            it("returns `NotificationFailed` with error code and error message") {
                assertThat(result).isEqualTo(NotificationFailed(errorCode, errorMessage))
            }
        }
    }
})