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  6. pytest.ini

U-Boot pytest suite


This tool aims to test U-Boot by executing U-Boot shell commands using the console interface. A single top-level script exists to execute or attach to the U-Boot console, run the entire script of tests against it, and summarize the results. Advantages of this approach are:

  • Testing is performed in the same way a user or script would interact with U-Boot; there can be no disconnect.
  • There is no need to write or embed test-related code into U-Boot itself. It is asserted that writing test-related code in Python is simpler and more flexible than writing it all in C.
  • It is reasonably simple to interact with U-Boot in this way.


The test suite is implemented using pytest. Interaction with the U-Boot console involves executing some binary and interacting with its stdin/stdout. You will need to implement various “hook” scripts that are called by the test suite at the appropriate time.

On Debian or Debian-like distributions, the following packages are required. Some packages are required to execute any test, and others only for specific tests. Similar package names should exist in other distributions.

PackageVersion tested (Ubuntu 14.04)

The test script supports either:

  • Executing a sandbox port of U-Boot on the local machine as a sub-process, and interacting with it over stdin/stdout.
  • Executing an external “hook” scripts to flash a U-Boot binary onto a physical board, attach to the board's console stream, and reset the board. Further details are described later.

Using virtualenv to provide requirements

Older distributions (e.g. Ubuntu 10.04) may not provide all the required packages, or may provide versions that are too old to run the test suite. One can use the Python virtualenv script to locally install more up-to-date versions of the required packages without interfering with the OS installation. For example:

$ cd /path/to/u-boot
$ sudo apt-get install python python-virtualenv
$ virtualenv venv
$ . ./venv/bin/activate
$ pip install pytest

Testing sandbox

To run the testsuite on the sandbox port (U-Boot built as a native user-space application), simply execute:

./test/py/ --bd sandbox --build

The --bd option tells the test suite which board type is being tested. This lets the test suite know which features the board has, and hence exactly what can be tested.

The --build option tells U-Boot to compile U-Boot. Alternatively, you may omit this option and build U-Boot yourself, in whatever way you choose, before running the test script.

The test script will attach to U-Boot, execute all valid tests for the board, then print a summary of the test process. A complete log of the test session will be written to ${build_dir}/test-log.html. This is best viewed in a web browser, but may be read directly as plain text, perhaps with the aid of the html2text utility.

Testing under a debugger

If you need to run sandbox under a debugger, you may pass the command-line option --gdbserver COMM. This causes two things to happens:

  • Instead of running U-Boot directly, it will be run under gdbserver, with debug communication via the channel COMM. You can attach a debugger to the sandbox process in order to debug it. See man gdbserver and the example below for details of valid values for COMM.
  • All timeouts in tests are disabled, allowing U-Boot an arbitrary amount of time to execute commands. This is useful if U-Boot is stopped at a breakpoint during debugging.

A usage example is:

Window 1:

./test/py/ --bd sandbox --gdbserver localhost:1234

Window 2:

gdb ./build-sandbox/u-boot -ex 'target remote localhost:1234'

Alternatively, you could leave off the -ex option and type the command manually into gdb once it starts.

You can use any debugger you wish, so long as it speaks the gdb remote protocol, or any graphical wrapper around gdb.

Some tests deliberately cause the sandbox process to exit, e.g. to test the reset command, or sandbox‘s CTRL-C handling. When this happens, you will need to attach the debugger to the new sandbox instance. If these tests are not relevant to your debugging session, you can skip them using pytest’s -k command-line option; see the next section.

Command-line options

  • --board-type, --bd, -B set the type of the board to be tested. For example, sandbox or seaboard.
  • --board-identity, --id set the identity of the board to be tested. This allows differentiation between multiple instances of the same type of physical board that are attached to the same host machine. This parameter is not interpreted by the test script in any way, but rather is simply passed to the hook scripts described below, and may be used in any site-specific way deemed necessary.
  • --build indicates that the test script should compile U-Boot itself before running the tests. If using this option, make sure that any environment variables required by the build process are already set, such as $CROSS_COMPILE.
  • --build-dir sets the directory containing the compiled U-Boot binaries. If omitted, this is ${source_dir}/build-${board_type}.
  • --result-dir sets the directory to write results, such as log files, into. If omitted, the build directory is used.
  • --persistent-data-dir sets the directory used to store persistent test data. This is test data that may be re-used across test runs, such as file- system images.

pytest also implements a number of its own command-line options. Commonly used options are mentioned below. Please see pytest documentation for complete details. Execute py.test --version for a brief summary. Note that U-Boot's script passes all command-line arguments directly to pytest for processing.

  • -k selects which tests to run. The default is to run all known tests. This option takes a single argument which is used to filter test names. Simple logical operators are supported. For example:
    • 'ums' runs only tests with “ums” in their name.
    • 'ut_dm' runs only tests with “ut_dm” in their name. Note that in this case, “ut_dm” is a parameter to a test rather than the test name. The full test name is e.g. “test_ut[ut_dm_leak]”.
    • 'not reset' runs everything except tests with “reset” in their name.
    • 'ut or hush' runs only tests with “ut” or “hush” in their name.
    • 'not (ut or hush)' runs everything except tests with “ut” or “hush” in their name.
  • -s prevents pytest from hiding a test‘s stdout. This allows you to see U-Boot’s console log in real time on pytest's stdout.

Testing real hardware

The tools and techniques used to interact with real hardware will vary radically between different host and target systems, and the whims of the user. For this reason, the test suite does not attempt to directly interact with real hardware in any way. Rather, it executes a standardized set of “hook” scripts via $PATH. These scripts implement certain actions on behalf of the test suite. This keeps the test suite simple and isolated from system variances unrelated to U-Boot features.

Hook scripts

Environment variables

The following environment variables are set when running hook scripts:

  • UBOOT_BOARD_TYPE the board type being tested.
  • UBOOT_BOARD_IDENTITY the board identity being tested, or na if none was specified.
  • UBOOT_SOURCE_DIR the U-Boot source directory.
  • UBOOT_TEST_PY_DIR the full path to test/py/ in the source directory.
  • UBOOT_BUILD_DIR the U-Boot build directory.
  • UBOOT_RESULT_DIR the test result directory.
  • UBOOT_PERSISTENT_DATA_DIR the test persistent data directory.


This script provides access to the U-Boot console. The script‘s stdin/stdout should be connected to the board’s console. This process should continue to run indefinitely, until killed. The test suite will run this script in parallel with all other hooks.

This script may be implemented e.g. by exec()ing cu, kermit, conmux, etc.

If you are able to run U-Boot under a hardware simulator such as qemu, then you would likely spawn that simulator from this script. However, note that u-boot-test-reset may be called multiple times per test script run, and must cause U-Boot to start execution from scratch each time. Hopefully your simulator includes a virtual reset button! If not, you can launch the simulator from u-boot-test-reset instead, while arranging for this console process to always communicate with the current simulator instance.


Prior to running the test suite against a board, some arrangement must be made so that the board executes the particular U-Boot binary to be tested. Often, this involves writing the U-Boot binary to the board's flash ROM. The test suite calls this hook script for that purpose.

This script should perform the entire flashing process synchronously; the script should only exit once flashing is complete, and a board reset will cause the newly flashed U-Boot binary to be executed.

It is conceivable that this script will do nothing. This might be useful in the following cases:

  • Some other process has already written the desired U-Boot binary into the board's flash prior to running the test suite.
  • The board allows U-Boot to be downloaded directly into RAM, and executed from there. Use of this feature will reduce wear on the board's flash, so may be preferable if available, and if cold boot testing of U-Boot is not required. If this feature is used, the u-boot-test-reset script should perform this download, since the board could conceivably be reset multiple times in a single test run.

It is up to the user to determine if those situations exist, and to code this hook script appropriately.

This script will typically be implemented by calling out to some SoC- or board-specific vendor flashing utility.


Whenever the test suite needs to reset the target board, this script is executed. This is guaranteed to happen at least once, prior to executing the first test function. If any test fails, the test infra-structure will execute this script again to restore U-Boot to an operational state before running the next test function.

This script will likely be implemented by communicating with some form of relay or electronic switch attached to the board's reset signal.

The semantics of this script require that when it is executed, U-Boot will start running from scratch. If the U-Boot binary to be tested has been written to flash, pulsing the board's reset signal is likely all this script need do. However, in some scenarios, this script may perform other actions. For example, it may call out to some SoC- or board-specific vendor utility in order to download the U-Boot binary directly into RAM and execute it. This would avoid the need for u-boot-test-flash to actually write U-Boot to flash, thus saving wear on the flash chip(s).

Examples contains some working example hook scripts, and may be useful as a reference when implementing hook scripts for your platform. These scripts are not considered part of U-Boot itself.

Board-type-specific configuration

Each board has a different configuration and behaviour. Many of these differences can be automatically detected by parsing the .config file in the build directory. However, some differences can't yet be handled automatically.

For each board, an optional Python module u_boot_board_${board_type} may exist to provide board-specific information to the test script. Any global value defined in these modules is available for use by any test function. The data contained in these scripts must be purely derived from U-Boot source code. Hence, these configuration files are part of the U-Boot source tree too.

Execution environment configuration

Each user‘s hardware setup may enable testing different subsets of the features implemented by a particular board’s configuration of U-Boot. For example, a U-Boot configuration may support USB device mode and USB Mass Storage, but this can only be tested if a USB cable is connected between the board and the host machine running the test script.

For each board, optional Python modules u_boot_boardenv_${board_type} and u_boot_boardenv_${board_type}_${board_identity} may exist to provide board-specific and board-identity-specific information to the test script. Any global value defined in these modules is available for use by any test function. The data contained in these is specific to a particular user's hardware configuration. Hence, these configuration files are not part of the U-Boot source tree, and should be installed outside of the source tree. Users should set $PYTHONPATH prior to running the test script to allow these modules to be loaded.

Board module parameter usage

The test scripts rely on the following variables being defined by the board module:

  • None at present.

U-Boot .config feature usage

The test scripts rely on various U-Boot .config features, either directly in order to test those features, or indirectly in order to query information from the running U-Boot instance in order to test other features.

One example is that testing of the md command requires knowledge of a RAM address to use for the test. This data is parsed from the output of the bdinfo command, and hence relies on CONFIG_CMD_BDI being enabled.

For a complete list of dependencies, please search the test scripts for instances of:

  • buildconfig.get(...
  • @pytest.mark.buildconfigspec(...

Complete invocation example

Assuming that you have installed the hook scripts into $HOME/ubtest/bin, and any required environment configuration Python modules into $HOME/ubtest/py, then you would likely invoke the test script as follows:

If U-Boot has already been built:

PATH=$HOME/ubtest/bin:$PATH \
    ./test/py/ --bd seaboard

If you want the test script to compile U-Boot for you too, then you likely need to set $CROSS_COMPILE to allow this, and invoke the test script as follow:

CROSS_COMPILE=arm-none-eabi- \
    PATH=$HOME/ubtest/bin:$PATH \
    ./test/py/ --bd seaboard --build

Writing tests

Please refer to the pytest documentation for details of writing pytest tests. Details specific to the U-Boot test suite are described below.

A test fixture named u_boot_console should be used by each test function. This provides the means to interact with the U-Boot console, and retrieve board and environment configuration information.

The function u_boot_console.run_command() executes a shell command on the U-Boot console, and returns all output from that command. This allows validation or interpretation of the command output. This function validates that certain strings are not seen on the U-Boot console. These include shell error messages and the U-Boot sign-on message (in order to detect unexpected board resets). See the source of for a complete list of “bad” strings. Some test scenarios are expected to trigger these strings. Use u_boot_console.disable_check() to temporarily disable checking for specific strings. See for an example.

Board- and board-environment configuration values may be accessed as sub-fields of the u_boot_console.config object, for example u_boot_console.config.ram_base.

Build configuration values (from .config) may be accessed via the dictionary u_boot_console.config.buildconfig, with keys equal to the Kconfig variable names.