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Chromium OS Unit Testing

Resources for writing unit tests

Running unit tests

We run unit tests as part of the build process using chromite's cros_run_unit_tests. In a nutshell, this script uses the portage method of building and running unit tests using FEATURES="test". To run all the Chromium OS unit tests, you can run cros_run_unit_tests directly from within your chroot. If you want to run just the unit tests for specific packages, you can use cros_run_unit_tests --packages "space-delimited list of portage package names". See cros_run_unit_tests --help for more information about other options.

As an example, let's say you just want to run the unit tests for the metrics package. To do so, you can run:

cros_run_unit_tests --board ${BOARD} --packages "metrics"

Running a single test

For platform2 packages, see the platform2 testing section.

For other packages that use gtest:

GTEST_ARGS="--gtest_filter=FreeDiskSpaceTest.*" cros_run_unit_tests --board ${BOARD} --packages google-breakpad

Adding unit tests

For packages using platform2, see the metrics ebuild as a good example of adding your unit test.

For packages using but not using platform2, it requires

  • Modifying the package ebuild (see example CL
    • create a src_test() stanza with appropriate gtest filters (see below), and add dependency of gtest and gmock
  • Modifying or (see example CL)
    • Add tests target and libraries.
  • Adding a testrunner (see example file)
    • If your package is of platform2, you don't need to add this manually. The canonical example is here.
  • Adding a * test file (see example file)
    • See gtest syntax and the usages from Google Test - Chromium's C++ test harness.

Regarding src_test() stanza, it is fine to have them build in the src_compile() stage as well. See also Portage documentation on src_test().

How to Blacklist a package from running its unit tests

It's discouraged to have unit tests that need to be blacklisted. However, if you really need to black list a package from running its unit tests as part of the build, use either RESTRCT="test" in your ebuild or add it to the unit tests blacklist in chromite.lib.portage_util.

Non-native architectures (e.g. QEMU)

Platform2 supports running unittests via qemu for non-native architectures (low level details can be found in this doc). The good news is that the process is the same as described above! Simply use cros_run_unit_tests for your board and specify the packages you want to run.


Sometimes qemu is not able to support your unittest due to using functionality not yet implemented. If you see errors like "qemu: unknown syscall: xxx", you'll need to filter that test (see below), and you should file a bug so we can update qemu.

Since qemu only works when run inside the chroot, only ebuilds that use the platform.eclass are supported currently.

Filtering tests in ebuilds

Packages using platform.eclass

Sometimes a test is flaky or requires special consideration before it'll work. You can do this by using the existing gtest filtering logic. For packages using platform.eclass, simply pass it as an argument to platform_test:

platform_pkg_test() {
    local gtest_filter=""

    platform_test "run" "${OUT}/some_testrunner" "0" "${gtest_filter}"

If you want to disable the tests for non-native arches, update the global knob:


Other Packages

If you want to filter gtests, you'll need to export the relevant gtest variables directly in your src_test function.

If you want to disable the tests for non-native arches, write your src_test like so:

src_test() {
    if ! use x86 && ! use amd64; then
        ewarn "Skipping unittests for non-native arches"
    ... existing test logic ...

Special Considerations

  • By default, cros_run_unit_tests will only use FEATURES="test" on packages that:
    • exist in the chromeos-base category
    • are in the dependency tree of virtual/target-os
    • have a src_test function