Interview with Will Lachance, Mozilla

Mozilla Firefox logo

Please introduce yourself.

Will Lachance, automation & tools developer. I work on automated systems for testing performance and correctness in Mozilla software (chiefly: Firefox, Firefox for Android, and FirefoxOS).

You can find out more about my group here.

How does development process look like? Do you have the same process for all Mozilla products or it is can be different?

It varies by project and group. In general our group has no formal process. People work on things that are priorities, checking in with other stakeholders (management, other groups, etc) regularly.

How many developers involved in the development of Firefox and Thunderbird?

Not sure what the current stat is. My guess would be a few hundred, directly and indirectly.

How does testing process look? Do you use regular testing?

Yes, we have a QA department.

What kind of testing do they use (performance, functional, compatibility, stability, unit testing etc)?

Yes, all of the above. :) I only work on automated performance and unit testing, so don’t know the specific details of what others are doing.

Do you test manually? Please tell more about each kind of testing.

Yes, we do manual testing but as I said I’m not completely familiar with how they work exactly.

What tests and testing frameworks do you use? Do developers create tests on regular basis for new functionality and bug fixes?

Yes, we have a large set of testing frameworks and a large number of tests that are running on every commit/change:

The most important ones are mochitest, reftest, and talos.

I heared you use instances in AWS for development and testing. Could you tell more?

Yup, we do. AWS is useful because we can scale our testing capacity up and down depending on demand. There’s many more things that need to be tested in the middle of the day when developers are busy.

Do you have own hardware servers?

Yes, for some types of testing (e.g. performance) we want to use real hardware with known performance characteristics.

What is the process for testing new features or significant changes?

We try to add automated tests to cover the new functionality. QA will generally do some manual testing as well.

Do you measure code coverage for Mozilla products? How often do you measure it? How much of code covered by auto tests?

I think so, but I am not sure of the details.

How do use Continuous Integration in development process?

We run tests on every commit. See

What is the process for releasing update with security fix?

Not sure of exact details. Googling for chemspill mozila( may tell you something.

Mozilla has big testing community. Please tell about involving volunteers in testing of Mozilla projects.

I can only speak for my team, but you can find some info here.

Who is responsible for releasing of new version? What are the release criterias?

Release engineering does the builds. Various parts of the organization do sign-off before it actually happens.

What was the most interesting bug in your practice?

I think the craziest one was tracking down why our Android test devices were rebooting after 15-20 minutes of run time. Turns out there was some long-forgotten code in the test agent app we used to communicate which was trying to ping some unreachable server. When they weren’t able to, they would assume that they had lost network connectivity and rebooted themselves. This was pretty deeply buried and not very well understood, took a while to go figure it out.

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