How Microsoft does Quality Assurance (QA)

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Microsoft has played an outsized role in the development and importance of quality assurance across the industry. Microsoft was the first major company to come up with a specialized testing role which went well beyond manual testing. In this issue, we cover:

  • The SDET role
  • Retiring of the SDET role

The SDET role

The SDET (Software Development Engineer in Test) role was one that Microsoft pioneered across the tech industry. They are software engineers who focused on writing automated tests; building and maintaining testing systems. The only difference between an SDET and a software development engineer (SDE) is that SDETs didn’t generally write production code: they wrote test code, working in the same team as SDEs.

I could not trace the exact introduction of the role, but it was most likely in the 1990s. For example, here’s a post from 2004 from a member of the Microsoft Exchange team explaining what it means to be an SDET in their organization:

“An SDET is a developer who works in a test team and not a development team. The SDET has a keen sense of a tester yet loves writing code, and lots of it.

The SDET enables the test team with the tools and processes that need to be in place for the testers to do what they do best… test the living daylights out of the product and find as many bugs as possible before it goes to the market.

An SDET has the ability to analyze the functionality and architecture of a Product and thus design and implement tools that help testers test it.

The SDET enjoys short project life cycles, designs and implements many tools and test frameworks in a single year, uses the latest technology and has plenty of room for innovation.

Though product quality is a prime concern, the SDET doesn’t have the stressful days that developers have during the end of a product life cycle. In layman’s terms… an SDET back-side is rarely on the line :)”

Microsoft had a formal career path for the SDET role. From the same post:

“There’s plenty of room for growth in [the SDET position.] If you love doing what you are doing as an SDET then you can grow to become a Test Architect. If you want to get involved in management, then you can progress towards becoming an SDET Lead and then Test Manager.

If you want to just code and not be involved with testing then you can take the path of becoming a developer. Many people take this path. If you realize that your heart belongs to testing, then you can become a tester.”

A 2:1 SDE:SDET ratio was common across Microsoft until around 2014. It was the case on my team at Skype for Xbox One, in 2012, when the team was formed. Here’s how our team was composed, based on headcount:

  • 12x SDEs (software development engineers)
  • 6x SDETs (software development engineer in test)
  • 2x PMs (product managers)
  • 1x EM (engineering manager)
  • 1x SDET lead

On our project, the SDET team owned all parts of testing:

  • Manually verifying that features devs built, worked as expected, including edge cases we might have not considered
  • Building integration and end-to-end tests to automate checks
  • Creating manual tests plans, and executing before major milestones
  • Being involved during the planning phase of features, bringing ideas on edge cases and how the work would be validated
  • Building solutions for tricky problems, such as how to do reliable performance benchmarking for our Skype product on the Xbox hardware

Unit tests were a source of tension, early on. Who should write them? Several experienced developers came from gaming, where developers typically don’t write automated tests, and their view was that any automation – including unit tests – should be done by the SDET teams. We cover more on how games are built in Game development basics, and go very hands-on in the issue, Building a simple game.

Those of us who’d previously built applications, or did test driven development (TDD,) felt that this approach was wrong, and that developers should write their own unit tests because unit tests and the code are tightly coupled. I was in this camp.

Having dedicated SDETs made it a tempting option for developers to “outsource” the writing of unit tests. I’m just going to say it now: without an SDET team, the question of who writes unit tests would have not been up for debate: we developers would have had to write them. This is a recurring debate I’ve seen in every team with assigned SDETs. Surprisingly, even this year I heard of a Silicon Valley-based company where a developer team has the test team write unit tests!

In our case, we settled on developers writing unit tests, with the SDET team doing everything else. This approach worked well enough, but there were a few memorable features of this setup:

  • An “us and them” dynamic that created division. When us developers finished a feature, we handed it over to an SDET, who usually found issues, so the feature came back to developers to fix. This felt annoying to devs, as it created work we might have not accounted for. Over time, it started to feel like there were two teams, with different goals, which didn’t always row in the same direction.
  • Ticket ping-pong between dev and test. I finish work on my feature and send it over to test (ping). The tester finds a bug and sends it back to me the next day (pong). I fix the bug, and send it over again in a few days (ping). The tester finds another bug and sends it back to me… and this back-and-forth happened more times than I’d be willing to admit!
  • Devs were good at building complex systems, and could help SDET a lot. Our SDET team had been building an integration testing system for months, and progress was slow. Our team really needed this system, as manual tests were taking too long. Finally, one of the senior engineers proposed that devs join in to help build this system, as one team. Two weeks later, with the lead of experienced devs, a system was up and running. This got me thinking; would the team not work better without the dev/test division? We had just proved it did.
  • The elephant in the room: some devs looked down on the SDET role. Although not everybody did, it was clear that many devs regarded SDET work as less challenging than their own. SDETs also knew they could have better career options by switching to a dev role.

Well, it turns out they didn’t have to wait that long for advancement.

Retiring the SDET role

Early 2014, I joined a new team called Skype for Web. This team was different from most teams at Skype, as they shipped a new version of the software every day, not every month.

The team consisted of 6 SDEs and 3 SDETs, on paper. In reality, we were 9 SDEs, thanks to the engineering manager and the test lead who quietly decided it made zero sense to have a dedicated test role, when we shipped new features every day. I write about this change that the team’s leadership didn’t broadcast, in the issue How Big Tech runs tech projects and the curious absence of Scrum:

“When I joined the Skype for Web team, we initially did two-week sprints, and followed the usual Scrum processes. We also had a split of software engineers and QA engineers. However, our shipping pace was every two weeks, but we wanted to ship more frequently.

The first thing we did was make QA a part of engineering. In the “old world”, an engineer would finish their work, check into their branch, update a ticket, and let the QA know it’s ready for review. The QA would take this ticket a day or two later, review it, and reopen the ticket if they found issues. This was a long delay.

We made a quiet, unofficial, change where all SDETs built production software as well, and all software engineers became responsible for testing their own code. Now, we no longer had to wait days for feedback before shipping code to production. However, the bi-weekly sprints and the numerous Scrum rituals became the next problem.”

We became a lot more productive by removing the SDET role from our team! SDETs still focused mainly on testing-related work, but also picked up development tasks. Just as importantly, we paired a lot! I remember pairing with SDETs to build a feature. I was good at thinking about how to make something work, and the SDET was really good at pointing out edge cases I hadn’t considered. When it came to debugging, the resourcefulness of SDETs surprised me.

On most teams across Microsoft, SDETs spent a lot of time manually testing things, and writing integration tests. But on our team there was very little manual testing, and we all built integration testing infrastructure, and monitoring infrastructure. When a developer or an SDET picked up a piece of work, they wrote all tests – unit and integration – which made sense.

The best part of this change was that there was no more “us vs them.” Arguments ceased about whether to fix a bug which an SDET had discovered, as now we did our own testing and fixed bugs which we discovered, before shipping to production.

Web teams across Microsoft started to quietly remove the SDET role. Back in 2014, our web team in the London Skype office felt ‘special,’ as the only other teams to merge the SDET function were web-based teams, of which there were not many. On every other team, SDETs kept working the way they always had.

However, it wasn’t only web teams within the Skype division which merged these roles for better efficiency. Web teams independently came to the realization that merging SDET and dev roles made them move faster, and so this happened across all of Microsoft!

In the middle of 2014, Microsoft formally retired the SDET role and introduced the SE role. The inspiration was apparently a larger web team at Microsoft, Bing. From Ars Technica, in 2014:

“At Bing, the task of creating programmatic tests was moved onto developers, instead of dedicated testers. QA still exists and is still important, but it performs end-user style "real world" testing, not programmatic automated testing. This testing has been successful for Bing, improving the team's ability to ship changes without harming overall software quality.”

In July 2014, Microsoft announced that they will execute their largest layoffs to that date, letting go 18,000 staff of the 127,000 employees at the company. 12,500 of the cuts were for the Nokia division. As part of this layoff, a large number of SDET roles were also eliminated. This happened around the same time as the SDET role was announced to be retired, and existing SDETs needed to move over to the software development engineer (SDE) track over the next several months. The SDE role was also renamed to SE – Software Engineer.

How did this transition work out? From what I gather, it went fine. The change made a lot of sense for teams that ship on a daily basis. And teams within Microsoft that ship weekly or monthly are increasingly rare, as Microsoft also leans into the software-as-a-service (SaaS) model. Of course, Microsoft continues to be a vendor for the Windows operating system family, and the Surface tablet. These are both areas where the approach to quality needs to be different to that of SaaS products.

A good account of the change came from the Visual Studio Team Services team in 2017, three years after this change. Reflecting on it, Brian Harry — currently Technical Fellow at Microsoft — wrote:

“Two years ago [in 2015], we had 10’s of thousands of tests. They were written by ‘testers’ to test code written by ‘developers’. While there were some advantages of this model – like clearly measurable and controllable investment in test, expertise and career growth in the testing discipline, etc., there were also many disadvantages – lack of accountability on the developers, slow feedback cycles (introduce bug, find bug, fix bug), developers had little motivation to make their code “testable”, divergence between code architecture and test architecture made refactoring and pivoting very hard/expensive, and more. (...)

Full testing would take the better part of a day to run, many more hours to “analyze the results” to identify false failures, and days or weeks to repair all the tests that were broken due to some legitimate change in the product. (...) Two years ago, we started on a path to completely redo testing.

We combined the dev and test orgs into a consolidated ‘engineering’ org. For the most part, we eliminated the distinction between people who code and people who test. That’s not to say every person does an identical amount of each, but every person does some of everything and is accountable for the quality of what they produce. We also set out to completely throw away our 10’s of thousands of tests that took 8 years to create, and replace them with new tests that were done completely differently.”

This team took stock of the type of tests they had in place and decided they didn’t like that there were few small unit tests, but lots of complex and hard to maintain end-to-end tests. So they changed this:

The change in the number and type of tests the Visual Studio Team Services experienced after merging the dev and the test teams. Before the merge: end-to-end tests dominated, but unit and integration tests were rare. This flipped after the merge. Data source: Microsoft Dev Blogs
The change in the number and type of tests the Visual Studio Team Services experienced after merging the dev and the test teams. Before the merge: end-to-end tests dominated, but unit and integration tests were rare. This flipped after the merge. Data source: Microsoft Dev Blogs

Here’s another visualization on how the team’s tests changed over a two-year timeframe:

In 2 years, almost all “old” tests from when test was separate from dev, were gone. The new tests became more granular as well. Data source: Microsoft Dev Blogs
In 2 years, almost all “old” tests from when test was separate from dev, were gone. The new tests became more granular as well. Data source: Microsoft Dev Blogs

So, was all this work worth it in the end? According to Brian, yes it was. Writing at the time, he said:

“We are starting to reap the benefits in improved quality, agility and engineer satisfaction.”

We covered the QA approach at one out of seven Big Tech companies from the article How Big Tech does QA. The full edition additionally covers details for:

  • Google
  • Google
  • Meta
  • Apple
  • Amazon
  • Uber
  • Netflix

Read the full issue here.

Related issues, which overlap with testing:


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