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.. _module-pw_unit_test:
``pw_unit_test`` unit testing library with a `Google Test`_-compatible API,
built on top of embedded-friendly primitives.
.. _Google Test:
``pw_unit_test`` is a portable library which can run on almost any system from
bare metal to a full-fledged desktop OS. It does this by offloading the
responsibility of test reporting and output to the underlying system,
communicating its results through a common interface. Unit tests can be written
once and run under many different environments, empowering developers to write
robust, high quality code.
``pw_unit_test`` is still under development and lacks many features expected in
a complete testing framework; nevertheless, it is already used heavily within
.. note::
This documentation is currently incomplete.
Writing unit tests
``pw_unit_test``'s interface is largely compatible with `Google Test`_. Refer to
the Google Test documentation for examples of to define unit test cases.
.. note::
A lot of Google Test's more advanced features are not yet implemented. To
request a feature addition, please
`let us know <>`_.
Using the test framework
The EventHandler interface
The ``EventHandler`` class in ``public/pw_unit_test/event_handler.h`` defines
the interface through which ``pw_unit_test`` communicates the results of its
test runs. A platform using ``pw_unit_test`` must register an event handler with
the unit testing framework to receive test output.
As the framework runs tests, it calls the event handler's callback functions to
notify the system of various test events. The system can then choose to perform
any necessary handling or aggregation of these events, and report them back to
the developer.
Predefined event handlers
Pigweed provides some standard event handlers upstream to simplify the process
of getting started using ``pw_unit_test``.
* ``SimplePrintingEventHandler``: An event handler that writes Google Test-style
output to a specified sink.
.. code::
[==========] Running all tests.
[ RUN ] Status.Default
[ OK ] Status.Default
[ RUN ] Status.ConstructWithStatusCode
[ OK ] Status.ConstructWithStatusCode
[ RUN ] Status.AssignFromStatusCode
[ OK ] Status.AssignFromStatusCode
[ RUN ] Status.CompareToStatusCode
[ OK ] Status.CompareToStatusCode
[ RUN ] Status.Ok_OkIsTrue
[ OK ] Status.Ok_OkIsTrue
[ RUN ] Status.NotOk_OkIsFalse
[ OK ] Status.NotOk_OkIsFalse
[ RUN ] Status.KnownString
[ OK ] Status.KnownString
[ RUN ] Status.UnknownString
[ OK ] Status.UnknownString
[==========] Done running all tests.
[ PASSED ] 8 test(s).
* ``LoggingEventHandler``: An event handler which uses the ``pw_log`` module to
output test results, to integrate with the system's existing logging setup.
.. _running-tests:
Running tests
To run unit tests, link the tests into a single binary with the unit testing
framework, register an event handler, and call the ``RUN_ALL_TESTS`` macro.
.. code:: cpp
#include "pw_unit_test/framework.h"
#include "pw_unit_test/simple_printing_event_handler.h"
void WriteString(const std::string_view& string, bool newline) {
if (newline) {
int main() {
pw::unit_test::SimplePrintingEventHandler handler(WriteString);
return RUN_ALL_TESTS();
Test filtering
If using C++17, filters can be set on the test framework to run only a subset of
the registered unit tests. This is useful when many tests are bundled into a
single application image.
Currently, only a test suite filter is supported. This is set by calling
``pw::unit_test::SetTestSuitesToRun`` with a list of suite names.
.. note::
Test filtering is only supported in C++17.
Build system integration
``pw_unit_test`` integrates directly into Pigweed's GN build system. To define
simple unit tests, set the ``pw_unit_test_MAIN`` build variable to a target
which configures the test framework as described in the :ref:`running-tests`
section, and use the ``pw_test`` template to register your test code.
.. code::
pw_test("foo_test") {
sources = [ "" ]
The ``pw_unit_test`` module provides a few optional libraries to simplify setup:
- ``simple_printing_event_handler``: When running tests, output test results
as plain text over ``pw_sys_io``.
- ``simple_printing_main``: Implements a ``main()`` function that simply runs
tests using the ``simple_printing_event_handler``.
- ``logging_event_handler``: When running tests, log test results as
plain text using pw_log (ensure your target has set a ``pw_log`` backend).
- ``logging_main``: Implements a ``main()`` function that simply runs tests
using the ``logging_event_handler``.
pw_test template
``pw_test`` defines a single unit test suite. It creates several sub-targets.
* ``<target_name>``: The test suite within a single binary. The test code is
linked against the target set in the build arg ``pw_unit_test_MAIN``.
* ``<target_name>.run``: If ``pw_unit_test_AUTOMATIC_RUNNER`` is set, this
target runs the test as part of the build.
* ``<target_name>.lib``: The test sources without ``pw_unit_test_MAIN``.
* All GN executable arguments are accepted and forwarded to the underlying
* ``enable_if``: Boolean indicating whether the test should be built. If false,
replaces the test with an empty target. Default true.
* ``test_main``: Target label to add to the tests's dependencies to provide the
``main()`` function. Defaults to ``pw_unit_test_MAIN``. Set to ``""`` if
``main()`` is implemented in the test's ``sources``.
.. code::
pw_test("large_test") {
sources = [ "" ]
enable_if = device_has_1m_flash
pw_test_group template
``pw_test_group`` defines a collection of tests or other test groups. It creates
several sub-targets:
* ``<target_name>``: The test group itself.
* ``<target_name>.run``: If ``pw_unit_test_AUTOMATIC_RUNNER`` is set, this
target runs all of the tests in the group and all of its group dependencies
* ``<target_name>.lib``: The sources of all of the tests in this group and its
* ``<target_name>.bundle``: All of the tests in the group and its dependencies
bundled into a single binary.
* ``<target_name>``: Automatic runner for the test bundle.
* ``tests``: List of the ``pw_test`` targets in the group.
* ``group_deps``: List of other ``pw_test_group`` targets on which this one
* ``enable_if``: Boolean indicating whether the group target should be created.
If false, an empty GN group is created instead. Default true.
.. code::
pw_test_group("tests") {
tests = [
pw_test("foo_test") {
# ...
pw_test("bar_test") {
# ...
pw_facade_test template
Pigweed facade test templates allow individual unit tests to build under the
current device target configuration while overriding specific build arguments.
This allows these tests to replace a facade's backend for the purpose of testing
the facade layer.
.. warning::
Facade tests are costly because each facade test will trigger a re-build of
every dependency of the test. While this sounds excessive, it's the only
technically correct way to handle this type of test.
.. warning::
Some facade test configurations may not be compatible with your target. Be
careful when running a facade test on a system that heavily depends on the
facade being tested.
RPC service
``pw_unit_test`` provides an RPC service which runs unit tests on demand and
streams the results back to the client. The service is defined in
``pw_unit_test_proto/unit_test.proto``, and implemented by the GN target
To set up RPC-based unit tests in your application, instantiate a
``pw::unit_test::UnitTestService`` and register it with your RPC server.
.. code:: c++
#include "pw_rpc/server.h"
#include "pw_unit_test/unit_test_service.h"
// Server setup; refer to pw_rpc docs for more information.
pw::rpc::Channel channels[] = {
pw::rpc::Server server(channels);
pw::unit_test::UnitTestService unit_test_service;
void RegisterServices() {
All tests flashed to an attached device can be run via python by calling
``pw_unit_test.rpc.run_tests()`` with a RPC client services object that has
the unit testing RPC service enabled. By default, the results will output via
.. code:: python
from pw_hdlc.rpc import HdlcRpcClient
from pw_unit_test.rpc import run_tests
PROTO = Path(os.environ['PW_ROOT'],
client = HdlcRpcClient(serial.Serial(device, baud), PROTO)
.. automodule:: pw_unit_test.rpc
:members: EventHandler, run_tests
Module Configuration Options
The following configurations can be adjusted via compile-time configuration of
this module.
The size of the memory pool to use for test fixture instances. By default this
is set to 16K.