Episode #10: Testable Serverless Applications with Slobodan Stojanović

About Slobodan Stojanović Slobodan Stojanović is CTO of Cloud Horizon, a software development studio based in Montreal Canada, and the CTO of Vacation Tracker. He is based in Belgrade and is the JS Belgrade meetup co-organizer. Slobodan is an AWS Serverless Hero, Claudia.js core team member, and co-author of "Serverless Applications with Node.js" book, published by Manning Publications. Twitter: @slobodan_ Vacation Tracker: vacationtracker.io Cloud Horizon: cloudhorizon.com Claudia.js: claudiajs.com Serverless Applications with Node.js: manning.com Blog: serverless.pub Transcript Jeremy: Hi, everyone. I'm Jeremy Daly and you're listening to Serverless Chats. This week, I'm chatting with Slobodan Stojanović. Hey, Slobodan. Thanks for joining me. Slobodan: Thanks for having me. Jeremy: So you're the CTO at Cloud Horizon and Vacation Tracker. So why don't you tell the listeners a bit about yourself and what these two companies do. Slobodan: Yeah, so for the last seven years, I’m a partner and CTO at Cloud Horizon. We basically do services for companies, and we build web applications for them. We worked with start ups and some enterprise companies and things like that. For a long time, we thought about, like, building a product. So last year, we finally started doing that. And we built a small tool that will help us to, so whenever our... we have, like, almost 30 people in the company and it's really hard for us now to track who is on a leave and who will be on a leave at some point. So we built a tool to help us out, to track just that. We don't need the full HR system and things like that. So we used serverless to build Vacation Tracker, our product, which is basically a slackbot and now web application that will help you to manage leaves for your company in just a few clicks, and people can request leaves through Slack and things like that. Besides that, I'm writing a lot about serverless. Not a lot in the last couple of weeks. But before that, I wrote a book about serverless called “Serverless Applications with Node.js” with my friend Aleksandar Simović and I have a couple of Medium posts and a few other articles that are explaining mostly testing architecture of serverless apps. So, that’s it, basically. Jeremy: Awesome. All right, so I wanted to talk about testing in serverless applications. And so maybe for people who are either new to development or, you know, are maybe used to different, ways of testing. I mean, why is testing so important? Let’s maybe start with that. Slobodan: Um, probably the best example I saw so far is the story, one of the stories from the previous book from Gojko Adzic called Humans vs Computers. So there was a guy somewhere in, I think, US that wanted to have custom plates for his car and he tried to fill out the form and he was into sales and boats and things like that. So, he had three choices in that form. First one was like ‘boat’, second one was ‘sailing’ and he didn't want the third choice, so he tried to leave it empty. He wasn't able to do that, so he typed ‘no plates’ or something like that. The first one was occupied, the second one was occupied, so he got ‘no plates’ plates. That was fun so he kept them and after a month, he started receiving a lot of tickets for parking because, you know, in the software for the guys that were filling the tickets for parking, no one predicted that there will be a guy with no custom plates or without plates. And whenever they don't get the plates, they just typed something. And most of time, they typed ‘no plates’ plates. So with testing, they would probably have handled that thing much before it hit the production and everything. So our applications are not perfect. There are so many things that when people start using, that can do in our applications. And when we start testing first we do some analytics of our application and think about the end users and the way that they will test our application. And on the other side, when our application grows really big it's easier for us to, like, be sure that we didn't break something. Unless we wanted to break it, of course. Jeremy: Right. And when people are building applications, too. I mean, this is something where I mean, I'm a big fan of test-driven development. Where you you actually write your tests first and then you write code to make the tests pass, right? Because then you know what the expected outcomes are, as opposed to, you know, kind of going back after the fact and trying to make some changes there. So, let's talk about testing with serverless, right? Let's get a little bit specific. So is there, or are there, different things that you need to do or, sort of, what's different about testing serverless versus maybe testing a traditional monolithic application? Slobodan: There are a few different things but, in general, testing is still the same. You want to check if your application works and the way that you want it to work. But some of the things are not your responsibility anymore. For example, infrastructure is, like, the responsibility of your vendor, such as AWS or Microsoft or someone else. So there's no point in really testing that part because that's not really something that, they have their own testing, things like that. But you still need to be sure that your business logic is working in a way that it works. And also all serverless applications are basically microservices, that they're working together. Most of the time, you don't have one monolithic application that is just uploaded to AWS Lambda or something like that. Most of the time, you have, like many different functions. For example, in Vacation Tracker we have, I think more than 80 functions now that they're working together. So it's really important to be sure that all those small services are working together the way we want them to work together, and that our end users have a decent experience and that they can use our application. Jeremy: Right. And so that the types of tests that you would run I mean, you're still gonna do unit testing, right? Slobodan: Yeah. So, basically, these types of tests are not that different. We still want to have unit tests because they are still the fastest. But, we also want to have integration tests, that are more important than ever, because we want to check if all these things work in integration, not just our code with the database, but maybe two different Lambda functions that are talking through some SNS topic or something like that. And of course, you wanted to have some kind of end-to-end tests. And maybe UI tests if your application is heavily using UI and things like that. So you still want to keep all these different types of testing that we had in previous non-serverless applications. Jeremy: So, the other thing I think that's important about UI tests and integration tests is with serverless, they're not quite as expensive as they were before, right? Slobodan: So yeah, one of the things that I used to kind of show that these testing pyramids. So, testing pyramid was defined by, I think Mike Cohn in his book Succeeding with Agile, a couple of years ago. Probably much more than that, actually, 10 years ago or something like that. So, ...