Yes, Docker can be used as a tool to help you out with some testing problems. Let me show an example of how it makes some load testing easier.

One of the projects I support at Mozilla is the push notification service that we run. Among the tests that I do for them is a load test using an internal tool that the developers of the service created. It is a Twisted application that runs using PyPy.

No, I do not know why they made those choices. Further more, it doesn't matter because I have to use it so I roll with the weirdness.

Installing it locally on my MacBook Pro was straightforward -- the docs even cover expected weirdness with some support libraries. But now that I have switched over to using Windows at work I ran into some difficulties getting all the dependencies installed in Windows Subsystem for Linux.

In fact, one of the developers uses Windows...and told me of the experience he had at failing to get it to work. "I just use VMWare Player and an Ubuntu VM".

I tried to get that working...and ran into a bunch of issues where I had to disable something called "Windows Defender Credential Guard". Which bugged me because I like to keep security mechanisms in place normally. I followed instructions FROM MICROSOFT on how to do it and VMWare Player still wouldn't run. Kept giving me the same error.

Okay, on to plan B -- Docker.

The first question was "how do I make this work?". I theorized I needed to do something like this:

• find a base container of Ubuntu 18
• get inside a running version of that image
• install all the required dependencies
• verify that the load testing tool works
• make a copy of that container
• push that copy up to Docker hub for teammates to use

Some searching revealed that I could get a running Ubuntu container and connect with it:

docker run --rm --it ubuntu

This downloaded the image and gave me access to it via a Bash shell.

With that shell, I started installing all the packages I would need to install the load testing tool, including adding the package repository for PyPy so I could install it with the package manager.

Once I got all the dependencies installed, I made sure that the tests could run. I even found out that there was a bug in the documenation. ;)

With a Docker image that had a working installation of the load testing tool, the next step turned out to be more straight forward than I had thought.

The Docker feature I needed was called snapshots. Here is what I did.

With the Docker container still running, I opened up another shell (in this case I am using Powershell) and used the command docker ps to get the name that had been assigned by Docker to my running container.

With that name I used the following command to save a version of that container:

docker commit name_of_container ubuntu:ap-loadtester 

Then I tagged the container so I can push up to Docker hub under my account:

docker tag ubuntu:ap-loadtester chartjes/ap-loadtester

Last, I pushed it up to Doker hub

docker push chartjes/ap-loadtester

So now I have:

• an Ubuntu container I can share
• that has all the dependencies installed
• can be used by teammates to load test the push service

Again, I emphasize that a tester with some programming experience can create some really useful testing tools by leveraging the same tools and environments used to build whatever you are testing.