Sprinting with pytest in Freiburg

On my way to the venue

Last week was the pytest development sprint located in the beautiful town of Freiburg, Germany. I had been really looking forward to the sprint, and being immediately after the Mozilla all-hands in London I was still buzzing with excitement when I started my journey to Freiburg.

On the first morning I really wasn’t sure about how to get to our sprint venue via public transport, and it didn’t seem to be far to walk from my hotel. It was a lovely sunny morning, and I arrived just in time for the introductions. Having been a pytest user for over five years I was already familiar with Holger, Ronny, and a few others, but this was the first time meeting them. We then spent some time planning out our first day, and coming up with things to work on throughout the week. My first activity was pairing up to work on pytest issues.

Breakfast at Cafe Schmidt
Breakfast at Cafe Schmidt

For my first task I paired with Daniel to work on an issue he had recently encountered, which I had also needed to workaround in latest versions of pytest. It turned out to be quite a complex issue related to determination of the root directory, which is used for relative reference to test files as well as a number of other things. The fix seemed simple at first – we just needed to exclude arguments that are not paths from consideration for determining the root directory, however there were a number of edge cases that needed resolving. The patch to fix this has not yet landed, but I’m feeling confident that it will be merged soon. When it does, I think we’ll be able to close at least three related issues!

Ducks in the town centre
Ducks in the town centre

Next, I worked with Bruno on moving a bunch of my plugins to the pytest-dev GitHub organisation. This allows any of the pytest core team to merge fixes to my plugins and means I’m not a blocker for any important bug fixes. I’m still intending on supporting the plugins, but it feels good to have a larger team looking after them if needed. The plugins I moved are pytest-selenium, pytest-html, pytest-variables, and pytest-base-url. Later in the week we also moved pytest-repeat with the approval of the author, who is happy for someone else to maintain the project.

If you’ve never used pytest, then you might expect to be able to simply run pytest  on the command line to run your tests. Unfortunately, this isn’t the case, and the reason is that the tool used to be part of a collection of other tools, all with a common prefix of py.  so you’d run your tests using the py.test command. I’m pleased to say that I worked with Oliver during the sprint to introduce pytest  as the recommended command line entry point for pytest. Don’t worry – the old entry point will still work when 3.0 is released, but we should be able to skip a bunch of confusion for new users!

Break day hikeOn Thursday we took a break and took a cable-car up a nearby peak and hiked around for a few hours. I also finally got an opportunity to order a slice of Schwarzwälder Kirschtorte (Black Forest gateau), which is named after the area and was a favourite of mine growing up. The break was needed after my brain had been working overtime processing the various talks, demonstrations, and discussions. We still talked a lot about the project, but to be out in the beautiful scenery watching para-gliders gracefully circling made for a great day.


When we returned to our sprint venue on Friday I headed straight into a bug triage with Tom, which ended up mostly focusing on one particular issue. The issue relates to hiding what is at first glance redundant information in the case of a failure, but on closer inspection there are actually many examples where this extra line in the explanation can be very useful.

Unfortunately I had to leave on Saturday morning, which meant I missed out on the final day of the sprint. I have to say that I can’t wait to attend the next one as I had so much fun getting to know everyone, learning some handy phrases in a number of different languages, and commiserating/laughing together in the wake of Brexit! I’m already missing my fellow sprinters!

Python testing sprint 2016

In June, the pytest developer community are gathering in Freiburg, Germany for a development sprint. This is being funded via an Indiegogo campaign, which needs your help to reach the goal! I am excited to say that I will be attending, which means that after over 5 years of using pytest, I’ll finally get to meet some of the core contributors.

I first learned about pytest when I joined Mozilla in late 2010. Much of the browser based automation at that time was either using Selenium IDE or Python’s unittest. There was a need to simplify much of the Python code, and to standardise across the various suites. One important requirement was the generation of JUnit XML reports (considered essential for reporting results in Jenkins) without compromising the ability to run tests in parallel. Initially we looked into nose, but there was an issue with this exact requirement. Fortunately, pytest didn’t have a problem with this – JUnit XML was supported in core and was compatible with the pytest-xdist plugin for running tests in parallel.

Ever since the decision to use pytest was made, I have not seen a compelling reason to switch away. I’ve worked on various projects, some with overly complex suites based on unittest, and I’ve always been grateful when I’ve been able to return to pytest. The active development of pytest has meant we’ve never had to worry about the project becoming unsupported. I’ve also always found the core contributors to be extremely friendly and helpful on IRC (#pylib on irc.freenode.net) whenever I need help. I’ve also more recently been following the pytest-dev mailing list.

I’ve recently written about the various plugins that we’ve released, which have allowed us to considerably reduce the amount of duplication between our various automation suites. This is even more critical as the Web QA team shifts some of the responsibility and ownership of some of their suites to the developers. This means we can continue to enhance the plugins and benefit all of the users at once, and our users are not limited to teams at Mozilla. The pytest user base is large, and that means our plugins are discovered and used by many. I always love hearing from users, especially when they submit their own enhancements to our plugins!

There are a few features I particularly like in pytest. Highest on the list is probably fixtures, which can really simplify setup and teardown, whilst keeping the codebase very clean. I also like being able to mark tests and use this to influence the collection of tests. One I find myself using a lot is a ‘smoke’ or ‘sanity’ marker, which collects a subset of the tests for when you can’t afford to run the entire suite.

During the sprint in June, I’d like to spend some time improving our plugins. In particular I hope to learn better ways to write tests for plugins. I’m not sure how much I’ll be able to help with the core pytest development, but I do have my own wishlist for improvements. This includes the following:

Maybe I’ll even be able to work on one of these, or any of the open issues on pytest with guidance from the experts in the room.