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This folder contains the web platform tests and the code required to integrate them with Servo. To learn how to write tests, go here.


In particular, this folder contains:

  • config.ini: some configuration for the web-platform-tests.
  • include.ini: the subset of web-platform-tests we currently run.
  • run the web-platform-tests in Servo.
  • web-platform-tests: copy of the web-platform-tests.
  • metadata: expected failures for the web-platform-tests we run.
  • mozilla: web-platform-tests that cannot be upstreamed.

Running the tests

The simplest way to run the web-platform-tests in Servo is ./mach test-wpt in the root directory. This will run the subset of JavaScript tests defined in include.ini and log the output to stdout.

A subset of tests may be run by providing positional arguments to the mach command, either as filesystem paths or as test urls e.g.

./mach test-wpt tests/wpt/web-platform-tests/dom/historical.html

to run the dom/historical.html test, or

./mach test-wpt dom

to run all the DOM tests.

There are also a large number of command line options accepted by the test harness; these are documented by running with --help.

Running all tests

Running all the WPT tests with debug mode results in a lot of timeout. If one wants to run all the tests, build with mach build -r and test with mach test-wpt --release

Running the tests without mach

When avoiding mach for some reason, one can run directly. However, this requires that all the dependencies for wptrunner are avaliable in the current python environment.

Running the tests manually

(See also the relevant section of the upstream README.)

It can be useful to run a test without the interference of the test runner, for example when using a debugger such as gdb.

To do this, first add the following to the system's hosts file:   www.web-platform.test   www1.web-platform.test   www2.web-platform.test   web-platform.test   xn--n8j6ds53lwwkrqhv28a.web-platform.test   xn--lve-6lad.web-platform.test

Then, navigate to tests/wpt/web-platform-tests. Next, create a directory, e.g. local-resources/, to contain a local copy of the resources/testharnessreport.js file. The version in the repository is actually a Python format string that has substitution done on it by harness/wptrunner/ to configure test output. Then, place a modified copy of the testharnessreport.js file in that directory, removing the format string variable:

mkdir local-resources
cp resources/testharnessreport.js local-resources/
$EDITOR local-resources/testharnessreport.js
# Replace `output:%(output)d` with `output:1` or `output:0`.

Now create a configuration file at config.json for the web-platform-tests server (configuration options you don't specify will be loaded from the defaults at config.default.json) with the following contents:

{"aliases": [
  {"url-path": "/resources/testharnessreport.js",
   "local-dir": "local-resources"

Finally, you can run python serve from tests/wpt/web-platform-tests. Then navigate Servo to http://web-platform.test:8000/path/to/test or https://web-platform.test:8443/path/to/test.

To prevent browser SSL warnings when running HTTPS tests locally, you will need to run Servo with --certificate-path resources/cert-wpt-only.

Running the tests in Firefox

When working with tests, you may want to compare Servo's result with Firefox. You can supply --product firefox along with the path to a Firefox binary (as well as few more odds and ends) to run tests in Firefox from your Servo checkout:

./mach test-wpt dom --product firefox --binary $GECKO_BINS/firefox --certutil-binary $GECKO_BINS/certutil --prefs-root $GECKO/testing/profiles

Updating test expectations

When fixing a bug that causes the result of a test to change, the expected results for that test need to be changed. This can be done manually, by editing the .ini file under the metadata folder that corresponds to the test. In this case, remove the references to tests whose expectation is now PASS, and remove .ini files that no longer contain any expectations.

When a larger number of changes is required, this process can be automated. This first requires saving the raw, unformatted log from a test run, for example by running ./mach test-wpt --log-raw /tmp/servo.log. Once the log is saved, run from the root directory:

./mach update-wpt /tmp/servo.log

Writing new tests

The simplest way to create a new test is to use the following command:

./mach create-wpt tests/wpt/path/to/new/test.html

This will create test.html in the appropriate directory using the WPT template for JavaScript tests. Tests are written using testharness.js. Documentation can be found here. To create a new reference test instead, use the following:

./mach create-wpt --reftest tests/wpt/path/to/new/reftest.html --reference tests/wpt/path/to/reference.html

reference.html will be created if it does not exist, and reftest.html will be created using the WPT reftest template. To know more about reftests, check this. These new tests can then be run in the following manner like any other WPT test:

./mach test-wpt tests/wpt/path/to/new/test.html
./mach test-wpt tests/wpt/path/to/new/reftest.html

Editing tests

web-platform-tests may be edited in-place and the changes committed to the servo tree. These changes will be upstreamed when the tests are next synced.

Updating the upstream tests

In order to update the tests from upstream use the same mach update commands. e.g. to update the web-platform-tests:

./mach update-wpt --sync
./mach test-wpt --log-raw=update.log
./mach update-wpt update.log

This should create two commits in your servo repository with the updated tests and updated metadata.

Servo-specific tests

The mozilla directory contains tests that cannot be upstreamed for some reason (e.g. because they depend on Servo-specific APIs), as well as some legacy tests that should be upstreamed at some point. When run they are mounted on the server under /_mozilla/.

Analyzing reftest results

Reftest results can be analyzed from a raw log file. To generate this run with the --log-raw option e.g.

./mach test-wpt --log-raw wpt.log

This file can then be fed into the reftest analyzer which will show all failing tests (not just those with unexpected results). Note that this ingests logs in a different format to original version of the tool written for gecko reftests.

The reftest analyzer allows pixel-level comparison of the test and reference screenshots. Tests that both fail and have an unexpected result are marked with a !.

Updating the WPT manifest

MANIFEST.json can be regenerated automatically with the mach command update-manifest e.g.

./mach update-manifest

This is equivalent to running

./mach test-wpt --manifest-update SKIP_TESTS