path: root/pw_unit_test/docs.rst

.. _module-pw_unit_test:

============
pw_unit_test
============
``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`_).

.. _GoogleTest: https://github.com/google/googletest

.. note::

   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 <https://google.github.io/googletest/>`_
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.

GoogleTest compatibility
========================
pw_unit_test implements a subset of GoogleTest. Supported features include:

* Test and test suite declarations.
* Most ``EXPECT`` and ``ASSERT`` macros, including ``EXPECT_OK`` and
  ``ASSERT_OK`` for functions returning a status.
* ``ASSERT_OK_AND_ASSIGN`` to test assigning a value when status is ``OK`` or
  fail the test.
* ``StatusIs`` matcher to expect a specific ``pw::Status`` other that ``OK``.
* ``IsOkAndHolds`` matcher to expect an object's status is ``OK`` and the value
  matches an expected value.
* Stream-style expectation messages, such as
  ``EXPECT_EQ(val, 5) << "Inputs: " << input``. Messages are currently ignored.

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

* Any GoogleMock features (e.g. :c:macro:`EXPECT_THAT`)
* Floating point comparison macros (e.g. :c:macro:`EXPECT_FLOAT_EQ`)
* Death tests (e.g. :c:macro:`EXPECT_DEATH`); ``EXPECT_DEATH_IF_SUPPORTED``
  does nothing but silently passes
* Value-parameterized tests

To request a feature addition, please `let us know
<mailto:pigweed@googlegroups.com>`_.

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

API Reference
-------------

Expectations
````````````
Expectations perform a check that when fails continues the test's execution
while still marking the test as a failure. They're particularly handy when
verifying multiple dimensions of the same feature so we can see all the errors
at the same time.

.. doxygendefine:: EXPECT_TRUE
.. doxygendefine:: EXPECT_FALSE
.. doxygendefine:: EXPECT_EQ
.. doxygendefine:: EXPECT_NE
.. doxygendefine:: EXPECT_GT
.. doxygendefine:: EXPECT_GE
.. doxygendefine:: EXPECT_LT
.. doxygendefine:: EXPECT_LE
.. doxygendefine:: EXPECT_NEAR
.. doxygendefine:: EXPECT_FLOAT_EQ
.. doxygendefine:: EXPECT_DOUBLE_EQ
.. doxygendefine:: EXPECT_STREQ
.. doxygendefine:: EXPECT_STRNE

Assertions
``````````
Assertions work exactly the same as expectations, but stop the execution of the
test as soon as a failed condition is met.

.. doxygendefine:: ASSERT_TRUE
.. doxygendefine:: ASSERT_FALSE
.. doxygendefine:: ASSERT_EQ
.. doxygendefine:: ASSERT_NE
.. doxygendefine:: ASSERT_GT
.. doxygendefine:: ASSERT_GE
.. doxygendefine:: ASSERT_LT
.. doxygendefine:: ASSERT_LE
.. doxygendefine:: ASSERT_NEAR
.. doxygendefine:: ASSERT_FLOAT_EQ
.. doxygendefine:: ASSERT_DOUBLE_EQ
.. doxygendefine:: ASSERT_STREQ
.. doxygendefine:: ASSERT_STRNE

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
:cpp:class:`pw::unit_test::GoogleTestStyleEventHandler` base.

.. code-block::

   [==========] 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).

.. cpp:namespace-push:: pw::unit_test

.. cpp:class:: GoogleTestStyleEventHandler

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

.. cpp:class:: SimplePrintingEventHandler : public GoogleTestStyleEventHandler

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

.. cpp: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.

.. cpp:class:: PrintfEventHandler : public GoogleTestStyleEventHandler

   Event handler that uses ``std::printf`` to output test results.

.. cpp:namespace-pop::

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.

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
:c:macro:`PW_UNIT_TEST_LINK_FILE_CONTAINING_TEST` macro to support running tests
in a static library.

.. c:macro:: PW_UNIT_TEST_LINK_FILE_CONTAINING_TEST(test_suite_name, test_name)

   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:

-------------
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.

.. code-block:: cpp

   #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) {
     printf("%s", string.data());
     if (newline) {
       printf("\n");
     }
   }

   int main() {
     // The following line has no effect with pw_unit_test_light, but makes this
     // test compatible with upstream GoogleTest.
     testing::InitGoogleTest();

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

Build system integration
========================
``pw_unit_test`` integrates directly into Pigweed's GN and CMake build systems.

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``.


GN
--
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-block::

   import("$dir_pw_unit_test/test.gni")

   pw_test("foo_test") {
     sources = [ "foo_test.cc" ]
   }

.. _module-pw_unit_test-pw_test:

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``.

**Arguments**

* 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.
* ``source_gen_deps``: List of target labels that generate source files used by
  this test. The labels must meet the constraints of GN's `get_target_outputs`,
  namely they must have been previously defined in the current file. This
  argument is required if a test uses generated source files and `enable_if` can
  evaluate to false.
* ``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``.
* ``test_automatic_runner_args``: Array of args to pass to automatic test
  runner. Defaults to ``pw_unit_test_AUTOMATIC_RUNNER_ARGS``.
* ``envvars``: Array of ``"key=value"`` strings representing environment
  variables to set when invoking the automatic test runner.

**Example**

.. code-block::

   import("$dir_pw_unit_test/test.gni")

   pw_test("large_test") {
     sources = [ "large_test.cc" ]
     enable_if = device_has_1m_flash
   }

.. _module-pw_unit_test-pw_test_group:

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>.bundle.run``: Automatic runner for the test bundle.

**Arguments**

* ``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.

**Example**

.. code-block::

   import("$dir_pw_unit_test/test.gni")

   pw_test_group("tests") {
     tests = [
       ":bar_test",
       ":foo_test",
     ]
   }

   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 disabled by default. To build and run facade tests, set the GN
arg :option:`pw_unit_test_FACADE_TESTS_ENABLED` to ``true``.

.. 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.

Build arguments
```````````````
.. option:: 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

.. option:: 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

.. option:: 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

.. option:: 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

.. option:: 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

.. option:: 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

.. option:: 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

.. option:: pw_unit_test_EXECUTABLE_TARGET_TYPE <template name>

   The name of the GN target type used to build pw_unit_test executables.

   Type: string (name of a GN template)
   Usage: toolchain-controlled only

.. option:: pw_unit_test_EXECUTABLE_TARGET_TYPE_FILE <gni file path>

   The path to the .gni file that defines pw_unit_test_EXECUTABLE_TARGET_TYPE.

   If pw_unit_test_EXECUTABLE_TARGET_TYPE is not the default of
   `pw_executable`, this .gni file is imported to provide the template
   definition.

   Type: string (path to a .gni file)
   Usage: toolchain-controlled only

.. option:: pw_unit_test_FACADE_TESTS_ENABLED <boolean>

   Controls whether to build and run facade tests. Facade tests add considerably
   to build time, so they are disabled by default.

.. option:: pw_unit_test_TESTONLY <boolean>

   Controls the `testonly` variable in pw_test, pw_test_group, and
   miscellaneous testing targets. This is useful if your test libraries (e.g.
   GoogleTest) used by pw_unit_test have the `testonly` flag set. False by
   default for backwards compatibility.

CMake
-----
pw_add_test function
````````````````````
``pw_add_test`` declares a single unit test suite. It creates several
sub-targets.

* ``{NAME}`` depends on ``${NAME}.run`` if ``pw_unit_test_AUTOMATIC_RUNNER`` is
  set, else it depends on ``${NAME}.bin``
* ``{NAME}.lib`` contains the provided test sources as a library target, which
  can then be linked into a test executable.
* ``{NAME}.bin`` is a standalone executable which contains only the test sources
  specified in the pw_unit_test_template.
* ``{NAME}.run`` which runs the unit test executable after building it if
  ``pw_unit_test_AUTOMATIC_RUNNER`` is set, else it fails to build.

**Required Arguments**

* ``NAME``: name to use for the produced test targets specified above

**Optional Arguments**

* ``SOURCES`` - source files for this library
* ``HEADERS``- header files for this library
* ``PRIVATE_DEPS``- private pw_target_link_targets arguments
* ``PRIVATE_INCLUDES``- public target_include_directories argument
* ``PRIVATE_DEFINES``- private target_compile_definitions arguments
* ``PRIVATE_COMPILE_OPTIONS``- private target_compile_options arguments
* ``PRIVATE_LINK_OPTIONS``- private target_link_options arguments

**Example**

.. code-block::

   include($ENV{PW_ROOT}/pw_unit_test/test.cmake)

   pw_add_test(my_module.foo_test
     SOURCES
       foo_test.cc
     PRIVATE_DEPS
       my_module.foo
   )

pw_add_test_group function
``````````````````````````
``pw_add_test_group`` defines a collection of tests or other test groups. It
creates several sub-targets:

* ``{NAME}`` depends on ``${NAME}.run`` if ``pw_unit_test_AUTOMATIC_RUNNER`` is
  set, else  it depends on ``${NAME}.bin``.
* ``{NAME}.bundle`` depends on ``${NAME}.bundle.run`` if
  ``pw_unit_test_AUTOMATIC_RUNNER`` is set, else it depends on
  ``${NAME}.bundle.bin``.
* ``{NAME}.lib`` depends on ``${NAME}.bundle.lib``.
* ``{NAME}.bin`` depends on the provided ``TESTS``'s ``<test_dep>.bin`` targets.
* ``{NAME}.run`` depends on the provided ``TESTS``'s ``<test_dep>.run`` targets
  if ``pw_unit_test_AUTOMATIC_RUNNER`` is set, else it fails to build.
* ``{NAME}.bundle.lib`` contains the provided tests bundled as a library target,
  which can then be linked into a test executable.
* ``{NAME}.bundle.bin`` standalone executable which contains the bundled tests.
* ``{NAME}.bundle.run`` runs the ``{NAME}.bundle.bin`` test bundle executable
  after building it if ``pw_unit_test_AUTOMATIC_RUNNER`` is set, else it fails
  to build.

**Required Arguments**

* ``NAME`` - The name of the executable target to be created.
* ``TESTS`` - ``pw_add_test`` targets and ``pw_add_test_group`` bundles to be
  included in this test bundle

**Example**

.. code-block::

   include($ENV{PW_ROOT}/pw_unit_test/test.cmake)

   pw_add_test_group(tests
     TESTS
       bar_test
       foo_test
   )

   pw_add_test(foo_test
     # ...
   )

   pw_add_test(bar_test
     # ...
   )

Build arguments
```````````````
.. option:: pw_unit_test_GOOGLETEST_BACKEND <target>

   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 (CMake target name)
   Usage: toolchain-controlled only

.. option:: 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 ``${NAME}`` and ``${NAME}.run`` targets 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 ``${NAME}`` will
   only build the unit test(s) and ``${NAME}.run`` will fail to build.

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

.. option:: 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

.. option:: pw_unit_test_AUTOMATIC_RUNNER_TIMEOUT_SECONDS <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

.. option:: pw_unit_test_ADD_EXECUTABLE_FUNCTION <function name>

   The name of the CMake function used to build pw_unit_test executables. The
   provided function must take a ``NAME`` and a ``TEST_LIB`` argument which are
   the expected name of the executable target and the target which provides the
   unit test(s).

   Type: string (name of a CMake function)
   Usage: toolchain-controlled only

.. option:: pw_unit_test_ADD_EXECUTABLE_FUNCTION_FILE <cmake file path>

   The path to the .cmake file that defines pw_unit_test_ADD_EXECUTABLE_FUNCTION.

   Type: string (path to a .cmake file)
   Usage: toolchain-controlled only

Bazel
-----
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_cc_test`` rule to register your
test code.

.. code-block::

   load("//pw_build:pigweed.bzl", "pw_cc_test")

   pw_cc_test(
       name = "foo_test",
       srcs = ["foo_test.cc"],
   }

.. _module-pw_unit_test-pw_cc_test:


pw_cc_test rule
```````````````
``pw_cc_test`` is a wrapper for `cc_test`_ that provides some defaults,
such as a dep on ``@pigweed//targets:pw_unit_test_main``. It supports and passes
through all the arguments recognized by ``cc_test``. Notably, tests can be
enabled or disabled using ``target_compatible_with``. For example, the following
test is skipped when `using upstream GoogleTest`_:

.. code-block::

   load("//pw_build:pigweed.bzl", "pw_cc_test")

   pw_cc_test(
       name = "no_upstream_test",
       srcs = ["no_upstream_test.cc"],
        target_compatible_with = select({
            "//pw_unit_test:light_setting": [],
            "//conditions:default": ["@platforms//:incompatible"],
        }),
   }

.. _cc_test: https://bazel.build/reference/be/c-cpp#cc_test


Build arguments
```````````````
.. option:: pw_unit_test_googletest_backend <target>

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

   Type: string (Bazel target label)
   Usage: toolchain-controlled only

.. option:: pw_unit_test_main <target>

   Implementation of a main function for ``pw_cc_test`` unit test binaries.

   Type: string (Bazel target label)
   Usage: toolchain-controlled only

Serial test runner
==================
To accelerate automated unit test bringup for devices with plain-text logging,
this module provides a serial-based test runner that triggers a device flash
and evaluates whether the test passed or failed based on the produced output.

pw_unit_test.serial_test_runner
-------------------------------
.. automodule:: pw_unit_test.serial_test_runner
   :members:
     DEFAULT_TEST_START_CHARACTER,
     SerialTestingDevice,
     run_device_test,

Setup
-----
To add support for a new device, implement a ``SerialTestingDevice`` class for
your device, and then configure your on-device firmware to wait to run unit
tests until ``DEFAULT_TEST_START_CHARACTER`` is sent over the serial connection.

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.

.. code-block:: 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::Channel::Create<1>(&my_output),
   };
   pw::rpc::Server server(channels);

   pw::unit_test::UnitTestService unit_test_service;

   void RegisterServices() {
     server.RegisterService(unit_test_services);
   }

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. This method returns a ``TestRecord`` dataclass instance, containing
the results of the test run.

.. code-block:: python

   import serial

   from pw_hdlc import rpc
   from pw_unit_test.rpc import run_tests

   PROTO = Path(
       os.environ['PW_ROOT'],
       'pw_unit_test/pw_unit_test_proto/unit_test.proto'
   )
   serial_device = serial.Serial(device, baud)
   with rpc.SerialReader(serial_device) as reader:
       with rpc.HdlcRpcClient(
           reader, PROTO, rpc.default_channels(serial_device.write)
       ) as client:
           run_tests(client.rpcs())

pw_unit_test.rpc
----------------
.. automodule:: pw_unit_test.rpc
   :members: EventHandler, run_tests, TestRecord

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

.. c:macro:: PW_UNIT_TEST_CONFIG_EVENT_BUFFER_SIZE

   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.

.. c:macro:: PW_UNIT_TEST_CONFIG_MEMORY_POOL_SIZE

   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
:ref:`third_party/googletest documentation <module-pw_third_party_googletest>`
for details.

When using upstream `GoogleTest`_ as the backend, the
:cpp:class:`pw::unit_test::GoogleTestHandlerAdapter` can be used in conjunction
with the above mentioned `EventHandler Interface <#the-eventhandler-interface>`_
and `Predefined event handlers`_. Included with this class is an implementation
of `RegisterEventHandler` that wraps event handlers in an adapter. This allows
the `main` functions written for `pw_unit_test:light` to work with upstream
GoogleTest without modification, as shown below.

.. code-block:: c++

   #include "gtest/gtest.h"
   #include "pw_unit_test/logging_event_handler.h"

   int main() {
     testing::InitGoogleTest();
     pw::unit_test::LoggingEventHandler logger;
     pw::unit_test::RegisterEventHandler(&logger);
     return RUN_ALL_TESTS();
   }

.. cpp:namespace-push:: pw::unit_test

.. cpp:class:: GoogleTestHandlerAdapter

   A GoogleTest Event Listener that fires GoogleTest emitted events to an
   appropriate ``EventHandler``.

.. cpp::namespace-pop::