AMA: why flaky tests for GTAC?

dmcnulla asks…

I enjoyed your GTAC presentation on “your tests are not flaky“. How did you pick your topic?

My response…

Firstly thanks for the compliment, you’re very kind.

When I came up for the topic I was working on a system where we were practicing continuous delivery by frequently doing production releases. As we began releasing more frequently the business expected this and so the reliability of our automated tests became more important. We wouldn’t release on a failed build since we were working on a high volume eCommerce site where a small bug could cause an outage costing a very large amount of revenue. We didn’t have a team of testers to fall back onto for any manual regression testing, so we were 100% dependent on our automated tests.

Even though we were clever about building testability into our system, we still had too many full-stack automated tests which would create non-deterministic results.

I believe everyone looks at the same thing slightly differently as we each have a unique lens that we see our world through and everyone’s lens has varying degrees of difference:

“Each of us tends to think we see things as they are, that we are objective. But this is not the case. We see the world, not as it is, but as we are—or, as we are conditioned to see it. When we open our mouths to describe what we see, we in effect describe ourselves, our perceptions, our paradigms.”

~ Stephen R. Covey

As people who were developing and maintaining tests, we were looking at our non-deterministic tests as the test’s fault. What we didn’t do was look through another lens to see that it could actually be the fault of our system as we had built it instead.

This aha! moment struck me when we released a bad build to production that had passed all automated QA by someone re-running our automated tests a number of times (to get them to pass).

We were blinded by perceived ‘test flakiness’: we refused to believe our problems were something else, so I thought it would be a good topic to present. From the feedback I received both at and after the event, it seems I am very much not alone.


Author: Alister Scott

Alister is an Excellence Wrangler for Automattic.