In production

These tests are found within the mozilla-central tree, along with the product code. They are all run when a changeset is pushed to mozilla-central, mozilla-inbound, or try, with the results showing up on Treeherder. They can also be run on their own.

The tests are run on machines in a very large pool. For the most part, all tests of a particular type run on the same pool of machines, regardless of branch. One substantial exception is that try builds are performed on a pool isolated from all other builds.

Linting

Lint tests help to ensure better quality, less error-prone code by analysing the code with a linter.

Functional testing

Table key

Symbol

Abbreviation for the test suite used by Treeherder. The first letter generally indicates which of the test harnesses is used to execute the test. The letter in parentheses identifies the actual test suite.

Name

Common name used when referring to the test suite.

File type

When adding a new test, you will generally create a file of this type in the source tree and then declare it in a manifest or makefile.

Platform

Most test suites are supported only on a subset of the available plaforms and operating systems. Unless otherwise noted:

• Desktop tests run on Windows, Mac OS X, and Linux.
• Mobile tests run on Android emulators or remotely on Android devices.

Process

• When Parent is indicated, the test file will always run in the parent process, even when the browser is running in Electrolysis (e10s) mode.
• When Child is indicated, the test file will run in the child process when the browser is running in Electrolysis (e10s) mode.
• The Allow label indicates that the test has access to mechanisms to run code in the other process.

Environment

• The JSShell and XPCShell environments are limited JavaScript execution environments with no windows or user interface (note however that XPCShell tests on Android are run within a browser window.)
• The Java environment is a limited Java execution environments with no user interface or connection to the Gecko rendering or JavaScript environment.
• The Content indication means that the test is run inside a content page loaded by a browser window.
• The Browser indication means that the test is loaded in the JavaScript context of a browser XUL window.
• The Browser Profile column indicates whether a browser profile is loaded when the test starts. The Allow label means that the test can optionally load a profile using a special command.

Privilege

Indicates whether the tests normally run with low (content) or high (chrome) JavaScript privileges. The Allow label means that the test can optionally run code in a privileged environment using a special command.

Performance testing

Talos is the framework used for performance testing. Up-to-date information on the set of tests and what they do can be found at https://wiki.mozilla.org/Performance_sheriffing/Talos/Tests

So which should I use?

Generally, you should pick the lowest-level framework that you can. If you are testing JavaScript but don't need a window, use XPCShell or even JSShell. If you're testing page layout, try to use Reftest. The advantage in lower level testing is that you don't drag in a lot of other components that might have their own problems, so you can home in quickly on any bugs in what you are specifically testing.

Here's a series of questions to ask about your work when you want to write some tests.

Is it low-level code?

If the functionality is exposed to JavaScript, and you don't need a window, consider XPCShell. If not, you'll probably have to use compiled-code tests, which can test pretty much anything but are difficult to write properly and are often less suitable than a domain-specific harness. In general, this should be your last option for a new test, unless you have to test something that is not exposed to JavaScript.

Does it cause a crash?

If you've found pages that crash Firefox, add a crashtest to make sure future versions don't experience this crash (assertion or leak) again. Note that this may lead to more tests once the core problem is found.

Is it a layout/graphics feature?

Reftest is your best bet, if possible.

Do you need to verify performance?

Use Talos!

Are you testing UI features?

If it's mobile UI, look into Robocop. For desktop, try browser chrome tests (soon to be split out of Mochitest), or Marionette if the application also needs to be restarted, or tested with localized builds.

Are you testing Mobile/Android?

For Mobile UI, look at Robocop. For Mobile features that are purely Java, look at android-test. There are some specific features that Mochitest or Reftest can cover. Browser-chrome tests do not run on Android. If you want to test performance, Talos runs fine with a few limitations (use the --noChrome options) and smaller cycles (e.g. 10 iterations instead of 20, etc.)

Are you doing none of the above?

• To get your tests run through buildbot, try Mochitest, or, if higher privileges are required, try Mochitest chrome tests.
• For Desktop Firefox, or if you just want to see the future of Gecko testing, look into the on-going Marionette project.

Need to get more data out of your tests?

Most test jobs now expose an environment variable named $MOZ_UPLOAD_DIR. If this variable is set during automated test runs, you can drop additional files into this directory, and they will be uploaded to a web server when the test finishes. The URLs to retrieve the files will be output in the test log.

Need to set preferences for test-suites?

First ask yourself if these prefs need to be enabled for all tests or just a subset of tests (e.g to enable a feature).

Setting prefs that only apply to certain tests

If the answer is the latter, try to set the pref as local to the tests that need it as possible. Here are some options:

• If the test runs in chrome scope (e.g mochitest chrome or browser-chrome), you can use Services.prefs to set the prefs in your test's setup function. Be sure to reset the pref back to its original value during teardown!
• Mochitest plain tests can use SpecialPowers to set prefs.

• All variants of mochitest can set prefs in their manifests. For example, to set a pref for all tests in a manifest:

  [DEFAULT]
  prefs =
    my.awesome.pref=foo,
    my.other.awesome.pref=bar,
  [test_foo.js]
  [test_bar.js]
  

• All variants of reftest can also set prefs in their manifests.
• All variants of web-platform-tests can also set prefs in their manifests.

Setting prefs that apply to the entire suite

Most test suites define prefs in user.js files that live under testing/profiles. Each directory is a profile that contains a user.js file with a number of prefs defined in it. Test suites will then merge one or more of these basic profiles into their own profile at runtime. To see which profiles apply to which test suites, you can inspect testing/profiles/profiles.json. Profiles at the beginning of the list get overridden by profiles at the end of the list.

Because this system makes it hard to get an overall view of which profiles are set for any given test suite, a handy profile utility was created:

$ cd testing/profiles
$ ./profile -- --help
usage: profile [-h] {diff,sort,show,rm} ...
$ ./profile show mochitest          # prints all prefs that will be set in mochitest
$ ./profile diff mochitest reftest  # prints differences between the mochitest and reftest suites