Test Manifests

Many test suites have their test metadata defined in files called test manifests.

Test manifests are divided into two flavors: ManifestParser Manifests and Reftest Manifests.

Naming Convention

The build system does not enforce file naming for test manifest files. However, the following convention is used.


For the plain flavor of mochitests.


For the chrome flavor of mochitests.


For the browser chrome flavor of mochitests.


For the a11y flavor of mochitests.


For xpcshell tests.

ManifestParser Manifests

ManifestParser manifests are essentially toml files that conform to a basic set of assumptions.

The reference documentation for manifestparser manifests describes the basic format of test manifests.

In summary, manifests are toml files with section names describing test files:


Keys under sections can hold metadata about each test:

skip-if = ["os == 'win'"]
skip-if = ["os == 'linux' && debug"]
fail-if = [
  "os == 'mac'",
  "os == 'android'",

There is a special DEFAULT section whose keys/metadata apply to all sections/tests:

property = value


In the above example, test_foo.js inherits the metadata property = value from the DEFAULT section.

Recognized Metadata

Test manifests can define some common keys/metadata to influence behavior. Those keys are as follows:


List of files that will be executed before the test file. (Used in xpcshell tests.)


List of files that will be executed after the test file. (Used in xpcshell tests.)


List of additional files required to run tests. This is typically defined in the DEFAULT section.

Unlike other file lists, support-files supports a globbing mechanism to facilitate pulling in many files with minimal typing. This globbing mechanism is activated if an entry in this value contains a * character. A single * will wildcard match all files in a directory. A double ** will descend into child directories. For example, data/* will match data/foo but not data/subdir/bar where data/** will match data/foo and data/subdir/bar.

Support files starting with / are placed in a root directory, rather than a location determined by the manifest location. For mochitests, this allows for the placement of files at the server root. The source file is selected from the base name (e.g., foo for /path/foo). Files starting with / cannot be selected using globbing.

Some support files are used by tests across multiple directories. In this case, a test depending on a support file from another directory must note that dependency with the path to the required support file in its own support-files entry. These use a syntax where paths starting with !/ will indicate the beginning of the path to a shared support file starting from the root of the srcdir. For example, if a manifest at dom/base/test/mochitest.toml has a support file, dom/base/test/server-script.sjs, and a mochitest in dom/workers/test depends on that support file, the test manifest at dom/workers/test/mochitest.toml must include !/dom/base/test/server-script.sjs in its support-files entry.


List of files that are generated as part of the build and don’t exist in the source tree.

The build system assumes that each manifest file, test file, and file listed in head, tail, and support-files is static and provided by the source tree (and not automatically generated as part of the build). This variable tells the build system not to make this assumption.

This variable will likely go away sometime once all generated files are accounted for in the build config.

If a generated file is not listed in this key, a clobber build will likely fail.


Record that this manifest duplicates another manifest.

The common scenario is two manifest files will include a shared manifest file via the ["include:file"] special section. The build system enforces that each test file is only provided by a single manifest. Having this key present bypasses that check.

The value of this key is ignored.


Skip this test if the specified condition is true. See Manifest Filter Language.

Conditions can be specified on multiple lines, where each line is implicitly joined by a logical OR (||). This makes it easier to add comments to distinct failures. For example:

skip-if = [
    "os == 'mac' && fission",  # bug 123 - fails on fission
    "os == 'windows' && debug",  # bug 456 - hits an assertion

Expect test failure if the specified condition is true. See Manifest Filter Language.

Conditions can be specified on multiple lines (see skip-if).


If present, the test should not be run in parallel with other tests.

Some test harnesses support parallel test execution on separate processes and/or threads (behavior varies by test harness). If this key is present, the test harness should not attempt to run this test in parallel with any other test.

By convention, the value of this key is a string describing why the test can’t be run in parallel.


Changes the scheme and domain from which the test runs. (Only used in mochitest suites)

There are two possible values:

Manifest Filter Language

Some manifest keys accept a special filter syntax as their values. These values are essentially boolean expressions that are evaluated at test execution time.

The expressions can reference a well-defined set of variables, such as os and debug. These variables are populated from the mozinfo.json file. For the full list of available variables, see the mozinfo documentation.

See the source for the full documentation of the expression syntax until it is documented here.

File Installation

Files referenced by manifests are automatically installed into the object directory into paths defined in mozbuild.frontend.emitter.TreeMetadataEmitter._process_test_manifest().

Relative paths resolving to parent directory (e.g. support-files = ../foo.txt have special behavior.

For support-files, the file will be installed to the default destination for that manifest. Only the file’s base name is used to construct the final path: directories are irrelevant. Files starting with / are an exception, these are installed relative to the root of the destination; the base name is instead used to select the file..

For all other entry types, the file installation is skipped.

Reftest Manifests

See MDN.