Web tests are used by Blink to test many components, including but not limited to layout and rendering. In general, web tests involve loading pages in a test renderer (content_shell) and comparing the rendered output or JavaScript output against an expected output file.
This document covers running and debugging existing web tests. See the Writing Web Tests documentation if you find yourself writing web tests.
Note that we changed the term “layout tests” to “web tests”. Please assume these terms mean the identical stuff. We also call it as “WebKit tests” and “WebKit layout tests”.
“Web platform tests” (WPT) are the preferred form of web tests and are located at web_tests/external/wpt. Tests that should work across browsers go there. Other directories are for Chrome-specific tests only.
Note: if you are looking for a guide for the Web Platform Test, you should read “Web platform tests” (WPT). This document does not cover WPT specific features/behaviors.
Note: if you are looking for a guide for running the Web Platform Tests with Chrome, Chrome Android or WebView, you should read “Running Web Platform Tests with run_wpt_tests.py”.
Android is not supported.
Before you can run the web tests, you need to build the blink_tests target to get content_shell and all of the other needed binaries.
autoninja -C out/Default blink_tests
On Mac, you probably want to strip the content_shell binary before starting the tests. If you don‘t, you’ll have 5-10 running concurrently, all stuck being examined by the OS crash reporter. This may cause other failures like timeouts where they normally don't occur.
strip ./out/Default/Content\ Shell.app/Contents/MacOS/Content\ Shell
The test runner script is in third_party/blink/tools/run_web_tests.py.
To specify which build directory to use (e.g. out/Default, etc.) you should pass the -t or --target parameter. If no directory is specified, out/Release will be used. To use the built-in out/Default, use:
third_party/blink/tools/run_web_tests.py -t Default
third_party\blink\tools\run_web_tests.bat instead.testing/xvfb.py; run_web_tests.py manages Xvfb itself.Tests marked as [ Skip ] in TestExpectations won't be run by default, generally because they cause some intractable tool error. To force one of them to be run, either rename that file or specify the skipped test on the command line (see below) or in a file specified with --test-list (however, --skip=always can make the tests marked as [ Skip ] always skipped). Read the Web Test Expectations documentation to learn more about TestExpectations and related files.
To run only some of the tests, specify their directories or filenames as arguments to run_web_tests.py relative to the web test directory (src/third_party/blink/web_tests). For example, to run the fast form tests, use:
third_party/blink/tools/run_web_tests.py fast/forms
Or you could use the following shorthand:
third_party/blink/tools/run_web_tests.py fast/fo\*
Example: To run the web tests with a debug build of content_shell, but only test the SVG tests and run pixel tests, you would run:
third_party/blink/tools/run_web_tests.py -t Default svg
As a final quick-but-less-robust alternative, you can also just use the content_shell executable to run specific tests by using (example on Windows):
out\Default\content_shell.exe --run-web-tests <url>|<full_test_source_path>|<relative_test_path>
as in:
out\Default\content_shell.exe --run-web-tests \ c:\chrome\src\third_party\blink\web_tests\fast\forms\001.html
or
out\Default\content_shell.exe --run-web-tests fast\forms\001.html
but this requires a manual diff against expected results, because the shell doesn't do it for you. It also just dumps the text result only (as the dump of pixels and audio binary data is not human readable). See Running Web Tests Using the Content Shell for more details of running content_shell.
To see a complete list of arguments supported, run:
third_party/blink/tools/run_web_tests.py --help
This script has a lot of command line flags. You can pass --help to the script to see a full list of options. A few of the most useful options are below:
| Option | Meaning |
|---|---|
--debug | Run the debug build of the test shell (default is release). Equivalent to -t Debug |
--nocheck-sys-deps | Don't check system dependencies; this allows faster iteration. |
--verbose | Produce more verbose output, including a list of tests that pass. |
--reset-results | Overwrite the current baselines (-expected.{png|txt|wav} files) with actual results, or create new baselines if there are no existing baselines. |
--fully-parallel | Run tests in parallel using as many child processes as the system has cores. |
--driver-logging | Print C++ logs (LOG(WARNING), etc). |
A test succeeds when its output matches the pre-defined expected results. If any tests fail, the test script will place the actual generated results, along with a diff of the actual and expected results, into src/out/Default/layout-test-results/, and by default launch a browser with a summary and link to the results/diffs.
The expected results for tests are in the src/third_party/blink/web_tests/platform or alongside their respective tests.
A test that runs but produces the wrong output is marked as “failed”, one that causes the test shell to crash is marked as “crashed”, and one that takes longer than a certain amount of time to complete is aborted and marked as “timed out”. A row of dots in the script's output indicates one or more tests that passed.
The TestExpectations file (and related files) contains the list of all known web test failures. See the Web Test Expectations documentation for more on this.
There are two ways to run web tests with additional command-line arguments:
third_party/blink/tools/run_web_tests.py --flag-specific=blocking-repaint
It requires that web_tests/FlagSpecificConfig contains an entry like:
{ "name": "blocking-repaint", "args": ["--blocking-repaint", "--another-flag"] }
This tells the test harness to pass --blocking-repaint --another-flag to the content_shell binary.
It will also look for flag-specific expectations in web_tests/FlagExpectations/blocking-repaint, if this file exists. The suppressions in this file override the main TestExpectations files. However, [ Slow ] in either flag-specific expectations or base expectations is always merged into the used expectations.
It will also look for baselines in web_tests/flag-specific/blocking-repaint. The baselines in this directory override the fallback baselines.
You can also use --additional-driver-flag to specify additional command-line arguments to content_shell, but the test harness won't use any flag-specific test expectations or baselines.
A virtual test suite can be defined in web_tests/VirtualTestSuites, to run a subset of web tests with additional flags, with virtual/<prefix>/... in their paths. The tests can be virtual tests that map to real base tests (directories or files) whose paths match any of the specified bases, or any real tests under web_tests/virtual/<prefix>/ directory. For example, you could test a (hypothetical) new mode for repainting using the following virtual test suite:
{ "prefix": "blocking_repaint", "platforms": ["Linux", "Mac", "Win"], "bases": ["compositing", "fast/repaint"], "args": ["--blocking-repaint"] }
This will create new “virtual” tests of the form virtual/blocking_repaint/compositing/... and virtual/blocking_repaint/fast/repaint/... which correspond to the files under web_tests/compositing and web_tests/fast/repaint, respectively, and pass --blocking-repaint to content_shell when they are run.
Note that you can run the tests with the following command line:
third_party/blink/tools/run_web_tests.py virtual/blocking_repaint/compositing \ virtual/blocking_repaint/fast/repaint
These virtual tests exist in addition to the original compositing/... and fast/repaint/... tests. They can have their own expectations in web_tests/TestExpectations, and their own baselines. The test harness will use the non-virtual expectations and baselines as a fallback. If a virtual test has its own expectations, they will override all non-virtual expectations. Otherwise the non-virtual expectations will be used. However, [ Slow ] in either virtual or non-virtual expectations is always merged into the used expectations. If a virtual test is expected to pass while the non-virtual test is expected to fail, you need to add an explicit [ Pass ] entry for the virtual test.
This will also let any real tests under web_tests/virtual/blocking_repaint directory run with the --blocking-repaint flag.
The “platforms” configuration can be used to skip tests on some platforms. If a virtual test suites uses more than 5% of total test time, we should consider to skip the test suites on some platforms.
The “prefix” value should be unique. Multiple directories with the same flags should be listed in the same “bases” list. The “bases” list can be empty, in case that we just want to run the real tests under virtual/<prefix> with the flags without creating any virtual tests.
A virtual test suite can have an optional exclusive_tests field to specify all (with "ALL") or a subset of bases tests that will be exclusively run under this virtual suite. The specified base tests will be skipped. Corresponding virtual tests under other virtual suites that don't specify the tests in their exclusive_tests list will be skipped, too. For example (unrelated fields are omitted):
{ "prefix": "v1", "bases": ["a"], } { "prefix": "v2", "bases": ["a/a1", "a/a2"], "exclusive_tests": "ALL", } { "prefix": "v3", "bases": ["a"], "exclusive_tests": ["a/a1"], }
Suppose there are directories a/a1, a/a2 and a/a3, we will run the following tests:
| Suite | a/a1 | a/a2 | a/a3 |
|---|---|---|---|
| base | skipped | skipped | run |
| virtual/v1 | skipped | skipped | run |
| virtual/v2 | run | run | n/a |
| virtual/v3 | run | skipped | run |
In a similar manner, a virtual test suite can also have an optional skip_base_tests field to specify all (with "ALL") or a subset of bases tests that will be run under this virtual while the base tests will be skipped. This will not affect other virtual suites.
{ "prefix": "v1", "bases": ["a/a1"], } { "prefix": "v2", "bases": ["a/a1"], "skip_base_tests": "ALL", }
Suppose there are directories a/a1 and a/a2 we will run the following tests:
| Suite | a/a1 | a/a2 |
|---|---|---|
| base | skipped | run |
| virtual/v1 | run | n/a |
| virtual/v2 | run | n/a |
For flags whose implementation is still in progress, flag-specific expectations and virtual test suites represent two alternative strategies for testing both the enabled code path and non-enabled code path. They are preferred to only setting a runtime enabled feature to status: "test" if the feature has substantially different code path from production because the latter would cause loss of test coverage of the production code path.
Consider the following when choosing between virtual test suites and flag-specific suites:
The waterfall builders and try bots will run all virtual test suites in addition to the non-virtual tests. Conversely, a flag-specific configuration won't automatically cause the bots to test your flag - if you want bot coverage without virtual test suites, you will need to follow these instructions.
Due to the above, virtual test suites incur a performance penalty for the commit queue and the continuous build infrastructure. This is exacerbated by the need to restart content_shell whenever flags change, which limits parallelism. Therefore, you should avoid adding large numbers of virtual test suites. They are well suited to running a subset of tests that are directly related to the feature, but they don't scale to flags that make deep architectural changes that potentially impact all of the tests.
Note that using wildcards in virtual test path names (e.g. virtual/blocking_repaint/fast/repaint/*) is not supported in run_web_tests.py command line , but you can still use virtual/blocking_repaint to run all real and virtual tests in the suite or virtual/blocking_repaint/fast/repaint/dir to run real or virtual tests in the suite under a specific directory.
Assuming you have already created a FlagSpecificConfig entry:
chromium.tests swarming pool and wait for approval.--flag-specific and possibly other special configurations (e.g., fewer shards).*-blink-rel builder's composition suite first (example).builders.json. rebaseline-cl and the WPT importer will now create baselines for that suite.FlagExpectations/.linux-rel or a dedicated builder like linux-blink-web-tests-force-accessibility-rel, which has customized location filters.All bugs, associated with web test failures must have the Test-Layout label. Depending on how much you know about the bug, assign the status accordingly:
When creating a new web test bug, please set the following properties:
You can also use the Layout Test Failure template, which pre-sets these labels for you.
After the web tests run, you should get a summary of tests that pass or fail. If something fails unexpectedly (a new regression), you will get a content_shell window with a summary of the unexpected failures. Or you might have a failing test in mind to investigate. In any case, here are some steps and tips for finding the problem.
http://localhost:8000/ and proceed from there.) The best tests describe what they‘re looking for, but not all do, and sometimes things they’re not explicitly testing are still broken. Compare it to Safari, Firefox, and IE if necessary to see if it‘s correct. If you’re still not sure, find the person who knows the most about it and ask.third_party/blink/tools/run_web_tests.py path/to/your/test.html produces a page listing all test results. Those which fail their expectations will include links to the expected result, actual result, and diff. These results are saved to $root_build_dir/layout-test-results.--results-directory=path/for/output/ option allows you to specify an alternative directory for the output to be saved to.file: URL.file: or http:) as the command argument in the Debugging section of the content_shell project Properties.--run-web-tests, followed by the URL (file: or http:) to your test. More information about running web tests in content_shell can be found here.TestShell::RunFileTest() call in content_shell_main.cc, or at shell->LoadURL() within RunFileTest() in content_shell_win.cc.Note: HTTP Tests mean tests under web_tests/http/tests/, which is a subset of WebKit Layout Tests originated suite. If you want to debug WPT's HTTP behavior, you should read “Web platform tests” instead.
To run the server manually to reproduce/debug a failure:
third_party/blink/tools/run_blink_httpd.py
The web tests are served from http://127.0.0.1:8000/. For example, to run the test web_tests/http/tests/serviceworker/chromium/service-worker-allowed.html, navigate to http://127.0.0.1:8000/serviceworker/chromium/service-worker-allowed.html. Some tests behave differently if you go to 127.0.0.1 vs. localhost, so use 127.0.0.1.
To kill the server, hit any key on the terminal where run_blink_httpd.py is running, use taskkill or the Task Manager on Windows, or killall or Activity Monitor on macOS.
The test server sets up an alias to the web_tests/resources directory. For example, in HTTP tests, you can access the testing framework using src="/js-test-resources/js-test.js".
Check https://test-results.appspot.com/ to see how a test did in the most recent ~100 builds on each builder (as long as the page is being updated regularly).
A timeout will often also be a text mismatch, since the wrapper script kills the content_shell before it has a chance to finish. The exception is if the test finishes loading properly, but somehow hangs before it outputs the bit of text that tells the wrapper it's done.
Why might a test fail (or crash, or timeout) on buildbot, but pass on your local machine?
chromium/src folder: third_party/blink/tools/run_web_tests.py --additional-driver-flag='--remote-debugging-port=9222' --additional-driver-flag='--remote-allow-origins=*' --additional-driver-flag='--debug-devtools' --timeout-ms=6000000out/Default/content_shell --remote-debugging-port=9222 --additional-driver-flag='--remote-allow-origins=*' --additional-driver-flag='--debug-devtools' --run-web-tests http://127.0.0.1:8000/path/to/test.htmlhttp://localhost:9222 in a stable/beta/canary Chrome, click the single link to open the devtools with the test loaded.test() in the console to actually start the test.NOTE: If the test is an html file, this means it's a legacy test so you need to add:
Add window.debugTest = true; to your test code as follows:
window.debugTest = true; function test() { /* TEST CODE */ }
https://crrev.com/c/5318502 implemented logging for inspector-protocol tests. With this CL for each test in stderr you should see Chrome DevTools Protocol messages that the test and the browser exchanged.
You can use this log to reproduce the failure or timeout locally.
Prepare a log file and ensure each line contains one protocol message in the JSON format. Strip any prefixes or non-protocol messages from the original log.
Make sure your local test file version matches the version that produced the log file.
Run the test using the log file:
third_party/blink/tools/run_web_tests.py -t Release \ --additional-driver-flag="--inspector-protocol-log=/path/to/log.txt" \ http/tests/inspector-protocol/network/url-fragment.js
You can use git bisect to find which commit broke (or fixed!) a web test in a fully automated way. Unlike bisect-builds.py, which downloads pre-built Chromium binaries, git bisect operates on your local checkout, so it can run tests with content_shell.
Bisecting can take several hours, but since it is fully automated you can leave it running overnight and view the results the next day.
To set up an automated bisect of a web test regression, create a script like this:
#!/bin/bash # Exit code 125 tells git bisect to skip the revision. gclient sync || exit 125 autoninja -C out/Debug -j100 blink_tests || exit 125 third_party/blink/tools/run_web_tests.py -t Debug \ --no-show-results --no-retry-failures \ path/to/web/test.html
Modify the out directory, ninja args, and test name as appropriate, and save the script in ~/checkrev.sh. Then run:
chmod u+x ~/checkrev.sh # mark script as executable git bisect start <badrev> <goodrev> git bisect run ~/checkrev.sh git bisect reset # quit the bisect session
See How to rebaseline.
See bugs with the component Blink>Infra for issues related to Blink tools, include the web test runner.
fast/dom/object-embed-plugin-scripting.html and plugins/embed-attributes-setting.html are expected to fail.