Expectation Data


For use in continuous integration systems, and other scenarios where regression tracking is required, wptrunner supports storing and loading the expected result of each test in a test run. Typically these expected results will initially be generated by running the testsuite in a baseline build. They may then be edited by humans as new features are added to the product that change the expected results. The expected results may also vary for a single product depending on the platform on which it is run. Therefore, the raw structured log data is not a suitable format for storing these files. Instead something is required that is:

  • Human readable

  • Human editable

  • Machine readable / writable

  • Capable of storing test id / result pairs

  • Suitable for storing in a version control system (i.e. text-based)

The need for different results per platform means either having multiple expectation files for each platform, or having a way to express conditional values within a certain file. The former would be rather cumbersome for humans updating the expectation files, so the latter approach has been adopted, leading to the requirement:

  • Capable of storing result values that are conditional on the platform.

There are few extant formats that meet these requirements, so wptrunner uses a bespoke expectation manifest format, which is closely based on the standard ini format.

Directory Layout

Expectation manifest files must be stored under the metadata directory passed to the test runner. The directory layout follows that of web-platform-tests with each test path having a corresponding manifest file. Tests that differ only by query string, or reftests with the same test path but different ref paths share the same reference file. The file name is taken from the last /-separated part of the path, suffixed with .ini.

As an optimisation, files which produce only default results (i.e. PASS or OK) don’t require a corresponding manifest file.

For example a test with url:


would have an expectation file


Generating Expectation Files

wptrunner provides the tool wptupdate to generate expectation files from the results of a set of baseline test runs. The basic syntax for this is:

wptupdate [options] [logfile]...

Each logfile is a structured log file from a previous run. These can be generated from wptrunner using the --log-raw option e.g. --log-raw=structured.log. The default behaviour is to update all the test data for the particular combination of hardware and OS used in the run corresponding to the log data, whilst leaving any other expectations untouched.

wptupdate takes several useful options:


Pull the latest version of web-platform-tests from the upstream specified in the config file. If this is specified in combination with logfiles, it is assumed that the results in the log files apply to the post-update tests.


Don’t attempt to check if the working directory is clean before doing the update (assuming that the working directory is a git or mercurial tree).


Create a a git commit, or a mq patch, with the changes made by wptupdate.


Overwrite all the expectation data for any tests that have a result in the passed log files, not just data for the same platform.


When updating test results, disable tests that have inconsistent results across many runs. This can precede a message providing a reason why that test is disable. If no message is provided, unstable is the default text.


When this option is used, the expected key (see below) stores expected intermittent statuses in addition to the primary expected status. If there is more than one status, it appears as a list. The default behaviour of this option is to retain any existing intermittent statuses in the list unless --remove-intermittent is specified.


This option is used in conjunction with --update-intermittent. When the expected statuses are updated, any obsolete intermittent statuses that did not occur in the specified logfiles are removed from the list.


Update the local copy of web-platform-tests without changing the expectation data and commit (or create a mq patch for) the result:

wptupdate --patch --sync

Update all the expectations from a set of cross-platform test runs:

wptupdate --no-check-clean --patch osx.log linux.log windows.log

Add expectation data for some new tests that are expected to be platform-independent:

wptupdate --no-check-clean --patch --ignore-existing tests.log

Manifest Format

The format of the manifest files is based on the ini format. Files are divided into sections, each (apart from the root section) having a heading enclosed in square braces. Within each section are key-value pairs. There are several notable differences from standard .ini files, however:

  • Sections may be hierarchically nested, with significant whitespace indicating nesting depth.

  • Only : is valid as a key/value separator

A simple example of a manifest file is:

root_key: root_value

  section_key: section_value

     subsection_key: subsection_value

  another_key: another_value

The web-platform-test harness knows about several keys:


Must evaluate to a possible test status indicating the expected result of the test. The implicit default is PASS or OK when the field isn’t present. When expected is a list, the first status is the primary expected status and the trailing statuses listed are expected intermittent statuses.


Any value indicates that the test is disabled.


The type of comparison for reftests; either == or !=.


The reference url for reftests.

Conditional Values

In order to support values that depend on some external data, the right hand side of a key/value pair can take a set of conditionals rather than a plain value. These values are placed on a new line following the key, with significant indentation. Conditional values are prefixed with if and terminated with a colon, for example:

  if cond1: value1
  if cond2: value2

In this example, the value associated with key is determined by first evaluating cond1 against external data. If that is true, key is assigned the value value1, otherwise cond2 is evaluated in the same way. If both cond1 and cond2 are false, the unconditional value3 is used.

Conditions themselves use a Python-like expression syntax. Operands can either be variables, corresponding to data passed in, numbers (integer or floating point; exponential notation is not supported) or quote-delimited strings. Equality is tested using == and inequality by !=. The operators and, or and not are used in the expected way. Parentheses can also be used for grouping. For example:

  if (a == 2 or a == 3) and b == "abc": value1
  if a == 1 or b != "abc": value2

Here a and b are variables, the value of which will be supplied when the manifest is used.

Expectation Manifests

When used for expectation data, manifests have the following format:

  • A section per test URL described by the manifest, with the section heading being the part of the test URL following the last / in the path (this allows multiple tests in a single manifest file with the same path part of the URL, but different query parts).

  • A subsection per subtest, with the heading being the title of the subtest.

  • A key expected giving the expectation value or values of each (sub)test.

  • A key disabled which can be set to any value to indicate that the (sub)test is disabled and should either not be run (for tests) or that its results should be ignored (subtests).

  • A key restart-after which can be set to any value to indicate that the runner should restart the browser after running this test (e.g. to clear out unwanted state).

  • A key fuzzy that is used for reftests. This is interpreted as a list containing entries like <meta name=fuzzy> content value, which consists of an optional reference identifier followed by a colon, then a range indicating the maximum permitted pixel difference per channel, then semicolon, then a range indicating the maximum permitted total number of differing pixels. The reference identifier is either a single relative URL, resolved against the base test URL, in which case the fuzziness applies to any comparison with that URL, or takes the form lhs url, comparison, rhs url, in which case the fuzziness only applies for any comparison involving that specific pair of URLs. Some illustrative examples are given below.

  • Variables debug, os, version, processor and bits that describe the configuration of the browser under test. debug is a boolean indicating whether a build is a debug build. os is a string indicating the operating system, and version a string indicating the particular version of that operating system. processor is a string indicating the processor architecture and bits an integer indicating the number of bits. This information is typically provided by mozinfo.

  • Top level keys are taken as defaults for the whole file. So, for example, a top level key with expected: FAIL would indicate that all tests and subtests in the file are expected to fail, unless they have an expected key of their own.

An simple example manifest might look like:

  type: testharness

  [Test something unsupported]
     expected: FAIL

  [Test with intermittent statuses]
     expected: [PASS, TIMEOUT]

  expected: ERROR

  disabled: http://test.bugs.example.org/bugs/12345

A more complex manifest with conditional properties might be:

    if os == "mac": FAIL
    if os == "windows" and version == "XP": FAIL

Note that PASS in the above works, but is unnecessary; PASS (or OK) is always the default expectation for (sub)tests.

A manifest with fuzzy reftest values might be:

  fuzzy: [10;200, ref1.html:20;200-300, subtest1.html==ref2.html:10-15;20]

In this case the default fuzziness for any comparison would be to require a maximum difference per channel of less than or equal to 10 and less than or equal to 200 total pixels different. For any comparison involving ref1.html on the right hand side, the limits would instead be a difference per channel not more than 20 and a total difference count of not less than 200 and not more than 300. For the specific comparison subtest1.html == ref2.html (both resolved against the test URL) these limits would instead be 10 to 15 and 0 to 20, respectively.