Hooking Android up to the (Selenium) Grid

Dave Hunt

When I set myself a Q4 goal of getting a small suite of Mozilla’s WebQA tests running on Android I didn’t think it would be much work. The AndroidDriver has been around for some time, and from what I understood it was pretty mature – I had even run a couple of tests locally against it and they worked well. What I found was there were a couple of important gotchas…

The first was that the port forwarding that’s necessary to run tests on an Android emulator or device binds to localhost. This isn’t a problem so long as the test commands originate from the same machine as the emulator/device is attached to, however that doesn’t make it very useful for Selenium Grid, where we want to run several emulators/devices remotely.

I was suprised that this issue had not come up before… I didn’t think I could possibly be the first person to want to hook up an AndroidDriver to Selenium Grid..! After searching around for a solution I decided to leave things for a while to take care of other priorities. I was then pulled back into the problem when my fellow Mozillian Raymond Etornam came across the same issue and was looking for a solution.

Raymond and I approached Dounia Berrada, who heads up the AndroidDriver efforts at Google, and as a result of this discussion, Raymond raised an issue in the Selenium project. Dounia got to the bottom of the issue and found a very simple solution, using socat to listen on another port on all interfaces and forward traffic to the localhost bound port forward configured by ADB. The Selenium project’s wiki has been updated with the solution.

The second issue I had was registering the AndroidDriver with Selenium Grid. This is simply a case of posting the correct JSON to the server, and is something that’s done for you when launching a Selenium server. The quick solution would have been to just start a Selenium server with the details for the Android node. This feels like too much of a hack, plus I didn’t really want the server running constantly when it’s not really doing anything other than consuming resources.

I decided to write a very simple Python package that would take a few arguments, construct the necessary JSON and post it to the Selenium Grid. I’ve released this as FlynnID (there’s a reference to ‘The Grid’ if you look hard enough) and it’s available on PyPI, with the source code on github.

A more long term solution will be to have the AndroidDriver register with a Selenium Grid when it’s started. If anyone is keen to look into this please get in touch!

So with these issues resolved, I was able to finally put together the first mobile test suite. I migrated the Input tests to WebDriver, did a lot of cleaning up, and split them into desktop/mobile tests. There’s only one mobile test there at the moment, but now we have everything in place we can go full speed into test development! If you’re interested in helping us out to write more tests or improve our frameworks/infrastructure then the WebQA page on QMO is a great place to start.

Oh, I’ve also added a cute Android icon  to Selenium Grid, which will be available from version 2.16.0.