Mocking and Testing AWS APIs with TestContainers and LocalStack

Cloud Computing is the default today. I do believe the future is containers and multi-cloud solutions. However today I work a lot with AWS. There are specific endpoints such as S3, AutoScaling, Route53 and other that are among the ones I use more in my day to day work. AWS API is easy to use however not no easy to test. Distributed systems tend to be hard to test. Having quick feedback is very important for engineers. There is some kind of tasks that need to interact with AWS APIs like S3 for backups for instance. However, if you need to wait to deploy in AWS to test it because is basically impossible to test it locally then we have a problem. We need to be able to do end-2-end testing however while you are coding or doing some troubleshooting is important to do things faster. There are 2 specific projects that can help us with this task. TestContainers and LocalStack. Today I will show to use LocalStack and TestContainers together with JUnit in order to do unit tests mocking S3 API. I will show how to do this using Java8. So Let's get started!

Running LocalStack locally

In order to run LocalStack locally we need to have Python and Docker installed. After you install them we can get and run LocalStack.



After you run LocalStack docker container make sure you shut down because when we run with TestContaoiners we will be able to do it over JUnit.

Setting Up Gradle Project

Now we need to set up a gradle project. Let's take a look at the build.gradle file.



Great. Now we can proceed and work with localstack and testcontainers together.

Hacking to use Latest LocalStack Image

There is a java project on TestContainers that does the Integration between LocalStack and TestContainers we will hack that project because we want to use the latest version of LocalStack. Right now the code is using an old version. So let's take a look at the code.



The changes I did above are quite simple - I just change the docker tag from 0.6 to latest and rename the name of class + enum and that's it.  Now we can move to testcontainers test code.

Testing S3 API and Running with TestConainers

Now we can focus on the unit test and mock S3. So let's go for it.



There are some important things here we need to cover. Let's start with the Annotation @Rule. This is important because the runner will use it when JUnit boot up and will boot up the Docker container needed. In regards to LocalStack as you can see I need to pass a Specific Service/Endpoint from AWS that we want to mock.

After the Rule we initialize AWS API - It's important to note here we are passing a custom endpoint otherwise we will reach the real AWS API. Then we can use S3 API normally and all commands will go to your Docker image. So we have mocked S3 Succesful. LocalStack support most of AWS endpoints and the combination with TestContainers is killer now is very easy to test AWS specific code.

The complete code is available on my GitHub here.

Cheers,
Diego Pacheco

Popular posts from this blog

C Unit Testing with Check

Image
When I start on IT, several years ago(+15), C was the first language that I learned. But was not the first language I mastered and deployed in production which was...surprisingly Visual Basic 6.0. However, when I learned C or any language back on that old and arcane time noddy was into testing. However now is impossible to work professionally in any language without tests. C is a low-level language but still kicks ass and has several interesting libs/frameworks. People use to fear C a lot because of lack of syntactical sugar but once you get used to it is not that hard at all. Today I want to show how you can do Unit Testing with C. I will not show how to do Unit Testing with C++ but with C ANSI actually. We will be using Check a unit test lib for C ANSI.
read more »

Having fun with Zig Language

Image
Zig is a general-purpose language created in 2016 by Andrew Kelly .  Zig aims to fix the issues C language has while being pragmatic and simple at the same time. Zig really shines as being simple by not having any hidden control flows, not having hidden memory allocations, no pre-processors, and no macros. Basically, it's one language and one language only. Since pre-processors and macros can get really complex and become their own universe. Sure it's not the Zig Philosophy.  Zig Compiler(Zig cc) also is a C compiler, and the interoperability from C to Zig is very good. Clearly, we can see influence from other languages like Go and Rust; however, Zig is pretty unique and different from Go and Rust.  Zig is fast. Zig is perfect for system programming. I bet we will see a lot of solutions being built in Zig. As a languages aficionado, I like to learn at least one language per year and sometimes more; Zig was my 2021 pick, did not regret it. Even if you dont use all language...
Keep reading

HMAC in Java

Image
In 2018 AWS CTO(Vogels) said : "Security is everyone's job". For the last 2 years, there was so many famous and big data leaks and breaks that made that statement be very true more than ever. Security often could mean worst performance and worst user experience so in order to get it right you really need to think about the designs before jumping into to code and consider performance and user experience has main requirements.  I was thinking about writing about how to do HMAC in Java for a while and recently Redis 6.0.0 come out and to my surprise, there was a refactoring on the password part in order to use HMAC.  Security easily could scare engineers often because it is not something well spread yet but I believe this will change soon. It does not matter if you have to deal with PII Data or not, security is super relevant because everybody is running their workloads at the cloud or with IoT and Edge devices which means more distribution, more code, more points of fail...
read more »