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Dump Accessibility Tests

There are several types of dump accessibility tests:

  • tree tests to test accessible trees;
  • node tests to test a single accessible node;
  • script tests to run a script and compare its output to expected results;
  • event tests to test accessible events.

All these tests are backed by the same engine and linked with the same idea: a test generates an output and then the output gets compared to expected results. Such approach has a great benefit: the tests can be rebaselined easily by making a test to generate expectations itself.

Tree tests are designed to test accessible tree. It loads an HTML file, waits for it to load, then dumps the accessible tree. The dumped tree is compared to an expectation file. The tests are driven by DumpAccessibilityTree testing class.

Node tests are used to run a test for a single node, for example, to check a specific property. The test loads an HTML file, waits for it to load, then dump a single accessible node for a DOM element whose id or class attribute is test. There is no support for multiple "test" nodes and the output will be for the first match located. The tests are driven by DumpAccessibilityNode testing class.

Script tests are used to run a script and test its output against expectations. The tests is driven by DumpAccessibilityScript testing class.

Event tests tests use a similar format but the events are dumped after the document finishes loading, and an optional go() function runs. See more on this below.

Each test is parameterized to run multiple times. Most platforms dump in the "blink" format (the internal data), and again in a "native" (platform-specific) format. The Windows platform has a second native format, "uia", so it runs a third time. The test name indicates which test pass was run, e.g., DumpAccessibilityTreeTest.TestName/blink. (Note: for easier identification, the Windows, Mac, Linux, and Android platforms rename the "native" pass to "win", "mac", "linux" and "android", respectively.)

The test output is a compact text representation of the accessible node(s) for that format, and it should be familiar if you're familiar with the accessibility protocol on that platform, but it's not in a standardized format - it's just a text dump, meant to be compared to expected output.

The exact output can be filtered so it only dumps the specific attributes you care about for a specific test.

Once the output has been generated, it compares the output to an expectation file in the same directory. If an expectation file for that test for that platform is present, it must match exactly or the test fails. If no expectation file is present, the test passes. Most tests don't have expectations on all platforms.

Compiling and running the tests

Most of the tests are hosted by content_browsertests testsuite.

autoninja -C out/Debug content_browsertests
out/Debug/content_browsertests --gtest_filter="All/DumpAccessibility*"

PDF accessibility tests though are running under browsertest testsuite.

autoninja -C out/Default browser_tests
out/Default/browser_tests --gtest_filter="PDFExtensionAccessibilityTreeDumpTest*"

File structure

  • foo.html -- a file to be tested
  • foo-expected-[platform].txt -- a file to be tested
  • foo-node-expected-[platform].txt - a a file containing a node test expectations

Supported platforms are:

  • android -- expected Android AccessibilityNodeInfo output
  • auralinux -- expected Linux ATK output
  • blink -- representation of internal accessibility tree
  • mac -- expected Mac NSAccessibility output
  • win -- expected Win IAccessible/IAccessible2 output
  • uia-win -- expected Win UIA output
  • uia-win7 -- expected Win7 UIA output (Version Specific Expected File)

Note, a single HTML test files can be used both for tree tests and node tests. In this case the expectations files for node tests portion will have an expectations-file qualifier of -node inserted immediately before expected. Thus for foo.html, there could be:

  • foo-expected-mac.txt -- expected Mac NSAccessibility output for the entire accessibility tree
  • foo-node-expected-mac.txt -- expected Mac NSAccessibility output for just the node in foo.html whose class is test

Expected files format

  • Blank lines and lines beginning with # are ignored
  • Skipped files: if first line of file begins with #<skip then the test passes. This can be used to indicate desired output with a link to a bug, or as a way to temporarily disable a test during refactoring.
  • Use 2 plus signs for indent to show hierarchy

Version Specific Expected Files

UIA sometimes differs between windows 7 and later versions of Windows. To account for these differences, the UIA accessibility tree formatter will look for a version specific expected file first: foo-expected-uia-win7.txt. If the version specific expected file does not exist, the normal expected file will be used instead: "foo-expected-uia-win.txt". There is no concept of version specific filters.

Directives

Directives allow you to control test flow and test output. The directives are defined inside the first comment block in the test's input file, one directive per line. For example, in the case of an HTML file the directives are located in between <!-- and -->, in the case of a PDF file the directives are preceding by % character designating a comment.

Directives have format of @directive_name:directive_value. Directives can be spawned over multiple lines:

@directive_name:
  directive_value
  directive_value

Certain directives are platform dependent. If so, then such directives are prefixed by a platform name:

  • @WIN- applied to Windows platform, MSAA/IAccessible2 APIs;
  • @UIA-WIN- applied to UIA on Windows;
  • @MAC- applied to Mac platform, NSAccessibility API;
  • @BLINK- applied to Chromium engine;
  • @ANDROID- applied to Android platform;
  • @AURALINUX- applied to Linux platform, ATK API.

Filters

By default only some attributes of nodes in the accessibility tree, or events fired (when running event tests), are output. This is to keep the tests robust and not prone to failure when unrelated changes affect the accessibility tree in unimportant ways.

You can use these filter types to match the attributes and/or attribute values you want included in the output.

  • -ALLOW filter means to include the attribute having non empty values;
  • -ALLOW-EMPTY filter means to include the attribute even if its value is empty;
  • -DENY filter means to exclude an attribute.

Filter directives are platform-dependent (see above).

Filters can contain simple wildcards (*) only, they're not regular expressions. Examples:

  • @WIN-ALLOW:name will output the name attribute on Windows
  • @WIN-ALLOW:name='Foo' will only output the name attribute if it exactly matches 'Foo'.
  • @WIN-DENY:name='X* will skip outputting any name that begins with the letter X.
  • @WIN-ALLOW:* to dump all attributes, useful for debuggin a test.

Scripting

Note: Mac platform is supported only.

Script tests provide platform dependent -SCRIPT directive to indicate a script to run. For example:

MAC-SCRIPT: input.AXName

to dump accessible name of an accessible node for a DOM element having input DOM id on Mac platform. You can also use :LINE_NUM syntax to indicate an accessible object, where LINE_NUM is index of a line where the accessible object is placed in the formatted tree.

Calls can be chained, for example:

input.AXFocusableAncestor.AXRole

Paramaterized attributes are also supported, for example:

textarea.AXPreviousWordStartTextMarkerForTextMarker({:3, 3, down})

You can also use array operator[] to refer to an array element at a given index, for example paragraph.AXChildren[0] will refer to the first child of the paragraph.

You can also rerieve anchor and focus text markers from a text marker range, for example:

p.AXTextMarkerRangeForUIElement(p).anchor

Advanced directives

Normally the system waits for the document to finish loading before running the test. You can tune the behavior up by the following directives.

@NO-LOAD-EXPECTED

Instructs to not wait for document load for url defined by the directive.

If you do not expect an iframe or object to load, (e.g. testing fallback), you can use the @NO-LOAD-EXPECTED: to cause the test to not wait for that frame to finish loading. For example the test would not wait for a url containing "broken.jpg" to load: @NO-LOAD-EXPECTED:broken.jpg <object data="./broken.jpg">Fallback</object

@WAIT-FOR

Delays a test unitl a string defined by the directive is present in the dump.

Occasionally you may need to write a dump tree test that makes some changes to the document before it runs the test. In that case you can use a special @WAIT-FOR: directive. It should be in an HTML comment, just like @ALLOW-WIN: directives. The WAIT-FOR directive just specifies a text substring that should be present in the dump when the document is ready. The system will keep blocking until that text appears.

You can add as many @WAIT-FOR: directives as you want, the test won't finish until all strings appear.

@EXECUTE-AND-WAIT-FOR

Delays a test until a string returned by a script defined by the directive is present in the dump.

You may also want to execute script and then capture a dump. Rather than use setTimeout and @WAIT-FOR:, consider using the @EXECUTE-AND-WAIT-FOR: directive. This directive expects a javascript function that returns a string to wait for. If a string is not returned, the tree dumper will not wait. @EXECUTE-AND-WAIT-FOR: directives are executed in order, after the document is ready and all @WAIT-FOR: strings have been found. Example: @EXECUTE-AND-WAIT-FOR: foo()

-RUN-UNTIL-EVENT

Indicates event recording should continue at least until a specific event has been received. This is a platform-dependent directive.

You may need to write an event test that keeps dumping events until a specific event line. In this case, use @WIN-RUN-UNTIL-EVENT (or similar for other platforms) with a substring that should occur in the event log, e.g., @WIN-RUN-UNTIL-EVENT:IA2_EVENT_TEXT_CARET_MOVED. Note that @*-RUN-UNTIL-EVENT is only used in dump events tests, and not used in dump tree tests.

If you add multiple @*-RUN-UNTIL-EVENT directives, the test will finish once any of them are satisfied. Note that any other events that come along with the last event will also be logged.

@DEFAULT-ACTION-ON

Invokes default action on an accessible object defined by the directive.

@NO_DUMP and @NO_CHILDREN_DUMP

To skip dumping a particular element, add @NO_DUMP to a property that will be exposed as an ax::mojom::StringAttribute, for example <div class="@NO_DUMP"></div>.

To skip dumping all children of a particular element, add @NO_CHILDREN_DUMP to a property that will be exposed as an ax::mojom::StringAttribute, for example <div class="@NO_CHILDREN_DUMP"></div>.

Note that setting the aria-label value to @NO_DUMP or @NO_CHILDREN_DUMP is not guaranteed to work due to certain roles no longer supporting author- provided naming in ARIA 1.2.

To load an iframe from a different site, forcing it into a different process, use /cross-site/HOSTNAME/ in the url, for example: <iframe src="cross-site/1.com/accessibility/html/frame.html"></iframe>

Generating expectations and rebaselining:

If you want to populate the expectation file directly rather than typing it or copying-and-pasting it, first make sure the file exists (it can be empty), then run the test with the --generate-accessibility-test-expectations argument, for example:

  out/Debug/content_browsertests \
    --generate-accessibility-test-expectations \
    --gtest_filter="All/DumpAccessibilityTreeTest.AccessibilityAriaAtomic/*"

This will replace the -expected-*.txt file with the current output. It's a great way to rebaseline a bunch of tests after making a change. Please manually check the diff, of course!

The * is a wildcard and will match any substring, in this case all platforms. To run on a single platform, replace the wildcard, e.g.:

  --gtest_filter="All/DumpAccessibilityTreeTest.AccessibilityAriaAtomic/linux"

For more information, see the detailed help with:

  out/Debug/content_browsertests --gtest_help

Note: For Android, generated expectations will replace the existing files on the test device. For example, if running on an emulator, for an ARIA test called my-test.html, the generated output can be found:

  /storage/emulated/0/chromium_tests_root/content/test/
     data/accessibility/aria/my-test-expected-android.txt

Adding a new test

If you are adding a new test file remember to add a corresponding test case in:

  • content/browser/accessibility/dump_accessibility_events_browsertest.cc; or
  • content/browser/accessibility/dump_accessibility_tree_browsertest.cc

More details on DumpAccessibilityEvents tests

These tests are similar to DumpAccessibilityTree tests in that they first load an HTML document, then dump something, then compare the output to an expectation file. The difference is that what's dumped is accessibility events that are fired.

To write a test for accessibility events, your document must contain a JavaScript function called go(). This function will be called when the document is loaded (or when the @WAIT_FOR directive passes), and any subsequent events will be dumped. Filters apply to events just like in tree dumps.

After calling go(), the system asks the page to generate a sentinel accessibility event - one you're unlikely to generate in your test. It uses that event to know when to "stop" dumping events. There isn't currently a way to test events that occur after some delay, just ones that happen as a direct result of calling go().

Duplicate Events on UIA

Windows will "translate" some IA2 events to UIA, and it is not possible to turn this feature off. Therefore as our UIA behavior is in addition to IA2, we will receive duplicated events for Focus, MenuOpened and MenuClosed.