Getting error while writing test cases for amazonSNS.publish() - unit-testing

Question

Src Code
class ReportingUtil {
companion object {
private val gson = Gson()
private val amazonSNS = AmazonSNSClientBuilder.standard().build()
private val topicArn = AppConfig.findString(TOPIC_ARN)
}
/**
* This function will convert object to json format and will publish to SNS topic.
* [invoiceData] -
*/
fun publishFailureInvoiceToSNS(invoiceData: InvoiceData) {
val jsonInvoiceMap = gson.toJson(invoiceData)
log.info("The Invoice : $invoiceData is converted to json format : $jsonInvoiceMap")
amazonSNS.publish(topicArn, jsonInvoiceMap)
log.info("Json invoice: $jsonInvoiceMap is published to the sns topic")
}
}
Unit Test
#Test
fun `test to publish invoice data to SNS topic`(){
initConfig()
val amazonSNS = mockk<AmazonSNS>()
val invoiceData = InvoiceData("a", "a", "a", BigDecimal(6), "a", "a", mutableMapOf("a" to "a"))
val reportingUtil = ReportingUtil()
every {
amazonSNS.publish("topicArn", "jsonInvoiceMap")
} returns PublishResult().withMessageId("MESSAGE_ID")
reportingUtil.publishFailureInvoiceToSNS(invoiceData)
}
This is giving me following error on src publish line,
com.amazonaws.services.sns.model.InvalidParameterException: Invalid
parameter: TopicArn or TargetArn Reason: no value for required
parameter (Service: AmazonSNS; Status Code: 400; Error Code:
InvalidParameter; Request ID: 5f1732ac-d63e-5e13-964c-65c312e218d7;
Proxy: null)
My use-case does not allow me to use dependency injection, therefore I made client static here.
I also want to add my custom optimization plans in catalyst which will also be triggered at build time. Is there any way to do all this before execution?

Answer 1

The amazonSNS you have mocked is not the one used to publish data in publishFailureInvoiceToSNS is not the one. So, when you call publishFailureInvoiceToSNS you are actually calling the real SNS API.
You have to refactor your code to use some kind of dependency injection. At least you should make it configurable. There are no use-cases that "does not allow to use DI".
If you're using JUnit 5, you could use these helpers for AWS clients injections in test. I would also recommend using localstack for unit tests.