Golang how to mock aws sns in a lambda integration test or unit test

Question

I want to local test lambda function call and not use aws sns service.

func Handler(request events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error){
    ...do some logic and db opeations.
    err := db.Create(something)
    if err != nil {
       msg := "something error."
       target := "sns:arn"
       // do sns notification
       sess := session.Must(session.NewSession())
       svc := sns.New(sess,&cfg)
       err = PublishNotification(svc, msg, target)
    }}

func PublishNotification(svc *sns.SNS, message string, target string) error {
      params := sns.PublishInput{
                Message:   &message,
                Subject:   &subject,
                TargetArn: &target,
}
      req, _ := svc.PublishRequest(&params)
      err := req.Send()
      if err != nil {
         return err
}
      return nil
}


func main(){
    lambda.Start(Handler)
}

Now Everything works fine. And I want to unit test or integration test this lambda handler.

func TestLabmdaWithSns(t *testing.T) {
        tests := []struct {
        request events.APIGatewayProxyRequest
}{
    request: events.APIGatewayProxyRequest{Body:"something"}
 }
 
 for _, test := range tests {
    response, err := Handler(test.request)
    // assert something
}

}

And I dont want to send sns notification when testing.
How should I mock this svc or PublishNotification function to not publish message to sns when local testing ?

Thanks.

Answer 1

You should use interface snsiface.SNSAPI instead of *sns.SNS in PublishNotification. Then you can inject mock implementation of snsiface.SNSAPI to the unit test as described here: https://docs.aws.amazon.com/sdk-for-go/api/service/sns/snsiface/