pw_unit_test provides a GoogleTest-compatible unit testing API for Pigweed. The default implementation is the embedded-friendly pw_unit_test:light backend. Upstream GoogleTest may be used as well (see Using upstream GoogleTest).


This documentation is currently incomplete.

pw_unit_test:light: GoogleTest for Embedded#

pw_unit_test:light implements a subset of GoogleTest with lightweight, embedded-friendly primitives. It is also highly portable and 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:light usage is the same as GoogleTest; refer to the GoogleTest documentation for examples of how to define unit test cases.

pw_unit_test:light is still under development and lacks many features expected in a complete testing framework; nevertheless, it is already used heavily within Pigweed.


Many of GoogleTest’s more advanced features are not yet implemented. Missing features include:

  • Any GoogleMock features (e.g. EXPECT_THAT)

  • Floating point comparison macros (e.g. EXPECT_FLOAT_EQ)

  • Death tests (e.g. EXPECT_DEATH); EXPECT_DEATH_IF_SUPPORTED does nothing but silently passes

  • Value-parameterized tests

To request a feature addition, please let us know.

See Using upstream GoogleTest below for information about using upstream GoogleTest instead.

The EventHandler interface#

The EventHandler class in public/pw_unit_test/event_handler.h defines the interface through which pw_unit_test:light communicates the results of its test runs. A platform using the pw_unit_test:light backend 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:light. All event handlers provide for GoogleTest-style output using the shared pw::unit_test::GoogleTestStyleEventHandler base.

[==========] 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).
class GoogleTestStyleEventHandler#

Provides GoogleTest-style output for pw_unit_test:light events. Must be extended to define how to output the results.

class SimplePrintingEventHandler : public GoogleTestStyleEventHandler#

An event handler that writes GoogleTest-style output to a specified sink.

class LoggingEventHandler : public GoogleTestStyleEventHandler#

An event handler which uses the pw_log module to output test results, to integrate with the system’s existing logging setup.

class PrintfEventHandler : public GoogleTestStyleEventHandler#

A C++14-compatible event handler that uses std::printf to output test results.

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.


Test filtering is only supported in C++17.

Tests in static libraries#

The linker usually ignores tests linked through a static library (.a file). This is because test registration relies on the test instance’s static constructor adding itself to a global list of tests. When linking against a static library, static constructors in an object file will be ignored unless at least one entity in that object file is linked.

Pigweed’s pw_unit_test implementation provides the PW_UNIT_TEST_LINK_FILE_CONTAINING_TEST macro to support running tests in a static library.

Ensures tests in a static library are linked and executed. Provide the test suite name and test name for one test in the file linked into a static library. Any test in the file may be used, but it is recommended to use the first for consistency. The test must be in a static library that is a dependency of this target. Referring to a test that does not exist causes a linker error.

Running tests#

To run unit tests, link the tests into a single binary with the unit testing framework, configure the backend if needed, and call the RUN_ALL_TESTS macro.

The following example shows how to write a main function that runs pw_unit_test with the light backend.

#include "gtest/gtest.h"

// pw_unit_test:light requires an event handler to be configured.
#include "pw_unit_test/simple_printing_event_handler.h"

void WriteString(const std::string_view& string, bool newline) {
  if (newline) {

int main() {
  // Since we are using pw_unit_test:light, set up an event handler.
  pw::unit_test::SimplePrintingEventHandler handler(WriteString);
  return RUN_ALL_TESTS();

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 Running tests section, and use the pw_test template to register your test 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 pw_executable.

  • 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.



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 individually.

  • <target_name>.lib: The sources of all of the tests in this group and its dependencies.

  • <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 depends.

  • enable_if: Boolean indicating whether the group target should be created. If false, an empty GN group is created instead. Default true.



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.


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.


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.

Build arguments#

pw_unit_test_GOOGLETEST_BACKEND <source_set>#

The GoogleTest implementation to use for Pigweed unit tests. This library provides “gtest/gtest.h” and related headers. Defaults to pw_unit_test:light, which implements a subset of GoogleTest.

Type: string (GN path to a source set) Usage: toolchain-controlled only

pw_unit_test_MAIN <source_set>#

Implementation of a main function for pw_test unit test binaries.

Type: string (GN path to a source set) Usage: toolchain-controlled only

pw_unit_test_AUTOMATIC_RUNNER <executable>#

Path to a test runner to automatically run unit tests after they are built.

If set, a pw_test target’s <target_name>.run action will invoke the test runner specified by this argument, passing the path to the unit test to run. If this is unset, the pw_test target’s <target_name>.run step will do nothing.

Targets that don’t support parallelized execution of tests (e.g. a on-device test runner that must flash a device and run the test in serial) should set pw_unit_test_POOL_DEPTH to 1.

Type: string (name of an executable on the PATH, or path to an executable) Usage: toolchain-controlled only

pw_unit_test_AUTOMATIC_RUNNER_ARGS <args>#

An optional list of strings to pass as args to the test runner specified by pw_unit_test_AUTOMATIC_RUNNER.

Type: list of strings (args to pass to pw_unit_test_AUTOMATIC_RUNNER) Usage: toolchain-controlled only

pw_unit_test_AUTOMATIC_RUNNER_TIMEOUT <timeout_seconds>#

An optional timeout to apply when running the automatic runner. Timeout is in seconds. Defaults to empty which means no timeout.

Type: string (number of seconds to wait before killing test runner) Usage: toolchain-controlled only

pw_unit_test_POOL_DEPTH <pool_depth>#

The maximum number of unit tests that may be run concurrently for the current toolchain. Setting this to 0 disables usage of a pool, allowing unlimited parallelization.

Note: A single target with two toolchain configurations (e.g. release/debug)

will use two separate test runner pools by default. Set pw_unit_test_POOL_TOOLCHAIN to the same toolchain for both targets to merge the pools and force serialization.

Type: integer Usage: toolchain-controlled only

pw_unit_test_POOL_TOOLCHAIN <toolchain>#

The toolchain to use when referring to the pw_unit_test runner pool. When this is disabled, the current toolchain is used. This means that every toolchain will use its own pool definition. If two toolchains should share the same pool, this argument should be by one of the toolchains to the GN path of the other toolchain.

Type: string (GN path to a toolchain) Usage: toolchain-controlled only

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 $dir_pw_unit_test:rpc_service.

The RPC service is primarily intended for use with the default pw_unit_test:light backend. It has some support for the GoogleTest backend, however some features (such as test suite filtering) are missing.

To set up RPC-based unit tests in your application, instantiate a pw::unit_test::UnitTestService and register it with your RPC server.

#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 logging.

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)


Utilities for running unit tests over Pigweed RPC.

class pw_unit_test.rpc.EventHandler#
abstract run_all_tests_end(passed_tests: int, failed_tests: int) None#

Called after the test run is complete.

abstract run_all_tests_start() None#

Called before all tests are run.

abstract test_case_disabled(test_case: pw_unit_test.rpc.TestCase) None#

Called when a disabled test case is encountered.

abstract test_case_end(test_case: pw_unit_test.rpc.TestCase, result: pw_unit_test.rpc.TestCaseResult) None#

Called when a test case completes with its overall result.

abstract test_case_expect(test_case: pw_unit_test.rpc.TestCase, expectation: pw_unit_test.rpc.TestExpectation) None#

Called after each expect/assert statement within a test case.

abstract test_case_start(test_case: pw_unit_test.rpc.TestCase) None#

Called when a new test case is started.

pw_unit_test.rpc.run_tests(rpcs: pw_rpc.client.Services, report_passed_expectations: bool = False, test_suites: Iterable[str] = (), event_handlers: Iterable[pw_unit_test.rpc.EventHandler] = (<pw_unit_test.rpc.LoggingEventHandler object>, ), timeout_s: Optional[Union[, float]] = UseDefault.VALUE) bool#

Runs unit tests on a device over Pigweed RPC.

Calls each of the provided event handlers as test events occur, and returns True if all tests pass.

Module Configuration Options#

The following configurations can be adjusted via compile-time configuration of this module.


The size of the event buffer that the UnitTestService contains. This buffer is used to encode events. By default this is set to 128 bytes.


The size of the memory pool to use for test fixture instances. By default this is set to 16K.

Using upstream GoogleTest#

Upstream GoogleTest may be used as the backend for pw_unit_test. A clone of the GoogleTest repository is required. See the third_party/googletest documentation for details.