CrOS EC (Embedded Controller)

Zephyr Testing

Before starting, developers should read the following:

Getting help

Get your tests reviewed by adding zephyr-test-eng@google.com as a reviewer on your CL.

Ask a question:

Where to add tests?

Tests currently reside in zephyr/test. When adding a new test it's possible to either create a new directory which includes a testcase.yaml or add a new entry to an existing testcase.yaml if the test is a slight variation of an existing test.

How to decide where your tests should go?

If you‘re adding a new compilational unit, check your dependencies. Is this unit tied to an existing Kconfig? If so, it’s possible that another test is already enabling it and linking your .c file. It's probably worth your time to simply add a new test suite to that existing test binary, or at the very least, creating a variant of the binary by adding a new entry in the testcase.yaml file.

If this doesn‘t work, it’s possible that you might need to create a new test from scratch. First, decide if this will be an integration test or a unit test. Integration tests will build the full system (see below) and thus are sometimes easier to set up (since they look and feel like an application). For the same reason that makes them easier to set up, the lack of mocks can make things more difficult when trying to force execution down a specific code path.

In the case of integration tests, any test under zephyr/test will serve as a good example. Alternatively, an example of a unit test can be found under common/spi/flash_reg.

The structure of the testcase.yaml

The top level testcase.yaml uses the test: block to define the attributes for each test case. The optional common: block uses the same attributes as the test cases, but the attributes are applied to all test cases in the file. See here for more details.

Some common attributes include:

  • extra_configs - a list of Kconfigs to add to the test.
  • extra_conf_files - specifies a YAML list of additional Kconfig files to to apply to the build. Replaces the CONF_FILE field in extra_args.
  • extra_overlay_confs - specifies a list of overlay Kconfig files. Replaces the OVERLAY_CONFIG field in extra_args.
  • extra_dtc_overlay_files - specifies a list of additional device tree files to apply to the build. Replaces the DTC_OVERLAY_FILE field in extra_args.

extra_args is a string field that allows injecting free-form CMake variables into the build. It is rarely needed and the practice of specifying CONF_FILE, OVERLAY_CONFIG, or DTC_OVERLAY_FILE here is deprecated. Please use the above fields for these functions, as they are much more readable.

Integration tests

Integration tests build the full EC. They require devicetree and all Kconfigs to be set appropriately. To build an integration test, simply use the following CMakeLists.txt template:

cmake_minimum_required(VERSION 3.20.0)
find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(<your_test_project_name>)
target_sources(app
  PRIVATE
    src/...
)

# Add global FFF declaration
add_subdirectory(${PLATFORM_EC}/zephyr/test/test_utils test_utils)

Then, you‘ll need a default prj.conf file to set the default configs. Keep in mind that this file will be automatically included in all the tests unless it is overridden by the test’s extra_args so you only want to put things that will apply to all tests here. It will look like:

CONFIG_ZTEST=y

# Enable the shim of the legacy CrosEC (You’ll need both)
CONFIG_CROS_EC=y
CONFIG_PLATFORM_EC=y

Mocking

We're using FFF for our mocking framework. For most use cases these are the things to remember:

  1. Reset your fakes in your test suite's before function using RESET_FAKE(). If multiple suites need to reset fakes, consider using a test rule.
  2. You'll need 1 instance of DEFINE_FFF_GLOBALS; in your binary. This is done in the sample above via including test_utils into your binary as a subdirectory.
  3. Use C++ for better custom_fake handling by setting the following before including fff.h:
    #define CUSTOM_FFF_FUNCTION_TEMPLATE(RETURN, FUNCNAME, ...) \
    std::function<RETURN(__VA_ARGS__)> FUNCNAME
    This will enable the following:
    ZTEST_F(suite, test_x)
{
  my_function_fake.custom_fake = [fixture]() {
    /* Capturing lambda has access to 'fixture' */
  };
  ...
}

Running twister

Run all tests under a specific directory

platform/ec$ ./twister -T path/to/my/tests

Run a specific test

platform/ec$ ./twister -s <test dir>/<my.test.scenario>

For example:

platform/ec$ ./twister -s drivers/drivers.default

Explanation of this string: drivers/ is the directory under zephyr/test/ that contains the requested test, and drivers.default is the specific test scenario specified in that directory's testcase.yaml file.

Run all tests with coverage

You can find more info on code coverage at Zephyr ztest code coverage.

platform/ec$ ./twister -p native_sim -p unit_testing --coverage

Get more info on twister

platform/ec$ ./twister --help

Other useful flags:

  • -i Print inline logs to STDOUT on error (as well as log file)
  • -n No clean (incremental builds)
  • -c Clobber, don't create a new twister-out/ directory
  • -v Verbose logging (can use -vv or -vvv for more logging)
  • -b Build only

Using assumptions

The zassume* API is used to skip tests when certain preconditions are not met. Please don‘t use it. In our tests we shouldn’t ever need to skip tests since we control all dependencies. If for some reason you actually need to skip a test use ztest_test_skip() since that will indicate that you intended to skip and didn't use assume by mistake when you meant to use assert.

Debugging

If the test targets native_sim or unit_testins platforms, you can run it through your choice of debugger (lldb is provided in the chroot). Additionally, it's possible to run only a subset of the tests via:

$ ./twister-out/native_sim/zephyr/test/.../zephyr/zephyr.exe -list
# List of all tests in the binary in the format of <suite_name:test_name>
$ ./twister-out/native_sim/zephyr/test/.../zephyr/zephyr.exe -test=suite0:*,suite1:test0
# Runs all tests under suite0 and test0 from suite1
$ lldb ./twister-out/unit_testing/.../testbinary
# Starts lldb for the test binary

Deflaking

zTest allows deflaking tests via shuffling. To enable this feature, simply turn on CONFIG_ZTEST_SHUFFLE=y. Your test binary's test suites and test order will be random as well as run multiple times. To fine-tune the execution:

  • Set CONFIG_ZTEST_SHUFFLE_SUITE_REPEAT_COUNT to an int controlling how many times the test suites will be shuffled and run.
  • Set CONFIG_ZTEST_SHUFFLE_TEST_REPEAT_COUNT to an int controlling how many times the individual tests will be shuffled and run (per suite run).

Note that the total number of times that tests will run is the result of multiplying those two Kconfig values.