Testing Extensions with Python

This guide covers the practical part of testing extensions with Python. Both for extensions developed in the kit repo and outside.

For information on testing extensions with C++ / doctest, look here, although there is some overlap, because it can be preferable to test C++ code from python bindings.

The Kit Sdk includes the omni.kit.test extension and a set of build scripts (in premake5-public.lua file) to run extension tests.

It supports two types of testing: * python tests (unittest with async/await support) * c++ tests (doctest)

It is generally preferred to test C++ code from python using bindings where feasible. In this way, the bindings are also tested, and that promotes writing bindings to your C++ code. Most of this guide focuses on python tests, but there is a C++ section at the very end.

Adding Extension Test: Build Scripts

If your extension’s premake5.lua file defines the extension project in usual way:

local ext = get_current_extension_info()
project_ext (ext)

It should already have corresponding bat/sh files generated in the _build folder, e.g.: _build\windows-x86_64\release\tests-[extension_name].bat

Even if you haven’t written any actual tests, it is already useful. It is a startup/shutdown test, that verifies that all extension dependencies are correct, python imports are working, and that it can start and exit without any errors.

An empty extension test entry is already an important one. Wrong or missing dependencies are a source of many future issues. Extensions are often developed in the context of certain apps and have implicit expectations. When used in other apps they do not work. Or when the extension load order randomly changes and other extensions you implicitly depend on start to load after you.

How does it work?

You can look inside Kit’s premake5-public.lua file to find the details on how it happens, follow the function project_ext(ext, args).

If you look inside that shell script, it basically runs an empty Kit + omni.kit.test + passes your extension. That will run the test system process which in turn will run another, tested process, which is basically: empty Kit + omni.kit.test + --enable [your extension].

The test system process prints each command it uses to spawn a new process. You can copy that command and use exactly the same command for debugging purposes.

You may ask why we spawn a process, which spawns another process? And both have omni.kit.test? Many reasons:

  1. Test system process monitors tested process:

    • It can kill it in case of timeout.

    • Reads return code. If != 0 indicates test failure.

    • Reads stdout/stderr for error messages.

  2. Test system process reads extension.toml of the tested extension in advance. That allows us to specify test settings, cmd args, etc.

  3. It can run many extension tests in parallel.

  4. It can download extensions from the registry before testing.

omni.kit.test has separate modules for both test system process (exttests.py) and tested process (unittests.py).

Writing First Test

Tested process runs with omni.kit.test which has the unittests module. It is a wrapper on top of python’s standard unittest framework.

It adds support for async/await usage in tests. Allowing test methods to be async and run for many updates/frames. For instance, a test can at any point call await omni.kit.app.get_app().next_update_async() and thus yield test code execution until next update.

All the methods in the python standard unittest can be used normally (like self.assertEqual etc).

If your extension for instance is defined:

name = "omni.foo"

Your tests must go into the omni.foo.tests module. The testing framework will try to import tests submodule for every python module, in order to discover them. This has a few benefits:

  1. It only gets imported in the test run. Thus it can use test-only dependencies or run more expensive code. There is no need to depend on omni.kit.test everywhere.

  2. It gets imported after other python modules. This way public modules can be imported and used in tests as if the tests are written externally (but still inside of an extension). In this way, the public API can be tested.

An actual test code can look like this:

#   omni.kit.test - python's standard library unittest module with additional wrapping to add support for async/await tests
#   For most things refer to the unittest docs: https://docs.python.org/3/library/unittest.html
import omni.kit.test

# Import extension python module we are testing with absolute import path, as if we are an external user (i.e. a different extension)
import example.python_ext

# Having a test class dervived from omni.kit.test.AsyncTestCase declared on the root of the module will make it auto-discoverable by omni.kit.test
class Test(omni.kit.test.AsyncTestCase):
    # Before running each test
    async def setUp(self):

    # After running each test
    async def tearDown(self):

    # Actual test, notice it is an "async" function, so "await" can be used if needed
    async def test_hello_public_function(self):
        result = example.python_ext.some_public_function(4)
        self.assertEqual(result, 256)

All the concepts here are from the standard unittest framework. Test methods start with test_. You need to inherit a base test class, which will be created, setUp() will be called before each test, tearDown() after. Everything can be async or “sync”.

Test Settings

Test Settings: Basics

The [[test]] section of extension.toml allows control of how to run a test process. We aim to make that configuration empty and for the defaults to be reasonable. We also strive to make tests run as close as possible to a real-usage run, making test environments the same as production.

However, you can specify which errors to ignore, what additional dependencies to bring, change the timeout, pass extra args etc. All the details are in Kit’s Extensions doc.

Below is an example, it shows how to:

  • add extra arguments

  • add test only dependencies (extensions)

  • change timeout

  • include and exclude error messages from failing tests

  args = ["--/some/setting=1"]
  dependencies = ["omni.kit.capture"]
  timeout = 666
  stdoutFailPatterns.include = ["*[error]*", "*[fatal]*"]
  stdoutFailPatterns.exclude = [
    "*Leaking graphics objects*",  # Exclude graphics leaks until fixed

Test Settings: Where to look for python tests?

By default test system process (exttests.py) reads all [[python.module]] entries from the tested extension and searches for tests in each of them. You can override it by explicitly setting where to look for tests:

pythonTests.include = ["omni.foo.*"]
pythonTests.exclude = ["omni.foo.bar.*"]

This is useful if you want to bring tests from other extensions. Especially, when testing apps.

Test Settings: Multiple test processes

Each [[test]] entry is a new process. Thus by default, each extension will run one test process to run all the python tests for that extension.

When adding multiple entries they must be named to distinguish them (in artifacts, logs, etc):

name = "basic"
pythonTests.include = [ "omni.foo.*basic*" ]

name = "other"
pythonTests.include = [ "omni.foo.*other*" ]

To select which process to run: pass -n [wildcard], where [wildcard] is a name. * are supported:

> _build\windows-x86_64\release\tests-example.python_ext.bat -n other

Test Settings: Disable test on certain platform

Any setting in extension.toml can be set per platform, using filters. Read more about them in “Extensions” doc. For example, to disable tests on Windows, the enabled setting can be overridden:

name = "some_test"
"filter:platform"."windows-x86_64".enabled = false

Running Your Test

To run your test just call the shell script described above: _build\windows-x86_64\release\tests-[extension_name].bat.

Run subset of tests

Pass -f [wildcard], where [wildcard] is a name of the test or part of the name. * are supported:

> _build\windows-x86_64\release\tests-example.python_ext.bat -f "public_function"

Run subset of tests using Tests Sampling

Pass --/exts/omni.kit.test/testExtSamplingFactor=N, where N is a number between 0.0 and 1.0, 0.0 meaning no tests will be run and 1.0 all tests will run and 0.5 means 50% of tests will run. To have this behavior on local build you need an additional parameter: --/exts/omni.kit.test/testExtSamplingContext='local'

> _build\windows-x86_64\release\tests-example.python_ext.bat --/exts/omni.kit.test/testExtSamplingFactor=0.5 --/exts/omni.kit.test/testExtSamplingContext='local'

Run tests from a file

To run tests from a file use --/exts/omni.kit.test/runTestsFromFile='' with the name of the file to read. Note: each time the tests run a playlist will be generated, useful to replay tests in a specific order or a subset of tests.

> _build\windows-x86_64\release\tests-example.python_ext.bat --/exts/omni.kit.test/runTestsFromFile='C:/dev/ov/kit/exttest_omni_foo_playlist_1.log'

Retry Strategy

There are 4 supported retry strategies:

  1. no-retry -> run tests once

  2. retry-on-failure -> run up to N times, stop at first success (N = testExtMaxTestRunCount)

  3. iterations -> run tests N times (N = testExtMaxTestRunCount)

  4. rerun-until-failure -> run up to N times, stop at first failure (N = testExtMaxTestRunCount)

For example to retry tests up to 3 times (if a flaky test occurs) use this command: > _build\windows-x86_64\release\tests-example.python_ext.bat --/exts/omni.kit.test/testExtRetryStrategy='retry-on-failure' --/exts/omni.kit.test/testExtMaxTestRunCount=3

Developing Tests

Pass --dev or --/exts/omni.kit.test/testExtUIMode=1. That will start a window with a list of tests instead of immediately running them. Here you can select tests to run. Change code, extension hot reloads, run again. E.g.:

> _build\windows-x86_64\release\tests-example.python_ext.bat --dev

Note that this test run environment is a bit different. Extra extensions required to render a basic UI are enabled.

Tests Code Coverage (Python)

Pass --coverage. That will run your tests and produce a coverage report at the end (HTML format):

> _build\windows-x86_64\release\tests-example.python_ext.bat --coverage

The output will look like this:

Generating a Test Report...
  > Coverage for example.python_ext:default is 49.8%
  > Full report available here C:/dev/ov/kit/kit/_testoutput/test_report/index.html

The HTML file will have 3 tabs. The coverage tab will display the coverage per file. Click on a filename to see the actual code coverage for that file.

Code Coverage

Based on the Google Code Coverage Best Practices the general guideline for extension coverage is defined as: 60% is acceptable, 75% is commendable and 90% is exemplary. The settings to modify the Coverage behavior are found in the extension.toml file of omni.kit.test, for example pyCoverageThreshold to modify the threshold and filter flags like pyCoverageIncludeDependencies to modify the filtering. Note: the python code coverage is done with Coverage.py. If you need to exclude code from Coverage you can consult this section.

The python code coverage is done with Coverage.py. If you need to exclude code from Coverage you can consult this section. For example any line with a comment # pragma : no cover is excluded. If that line introduces a clause, for example, an if clause, or a function or class definition, then the entire clause is also excluded.

    if example:  # pragma: no cover
        print("this line and the `if example:` branch will be excluded")
    print("this line not excluded")

Debugging Coverage

If you see strange coverage results, the easiest way to understand what is going is to modify test_coverage.py from omni.kit.test. In def startup(self) comment out the source=self._settings.filter line and also remove all items in self._coverage.config.disable_warnings. Coverage will run without any filter and will report all warnings, giving more insights. List of warnings can be seen here.

Disabling a python test

Use decorators from unittest module, e.g.:

    @unittest.skip("Fails on Linux now, to be fixed")  # OM-12345
    async def test_create_delete(self):

Pass extra cmd args to the test

To pass extra arguments for debugging purposes (for permanent use [[test]] config part) there are 2 ways:

  • all arguments after -- will be passed, e.g. _build\windows-x86_64\release\tests-[extension_name].bat -- -v --/app/printConfig=1

  • use /exts/omni.kit.test/testExtArgs setting, e,g,: --/exts/omni.kit.test/testExtArgs/0="-v"

Choose an app to run tests in

All tests run in a context of an app, which by default is an empty app: "${kit}/apps/omni.app.test_ext.kit". You can instead pass your own kit file, where you can define any extra settings.

In this kit file you can change testing environment, enable some debug settings or extensions. omni.app.test_ext_kit_sdk.kit app kit comes with a few useful settings commented.

Test Output

For each test process, omni.kit.test provides a directory it can write test outputs to (logs, images, etc):

import omni.kit.test
output_dir = omni.kit.test.get_test_output_path()

Or using test_output token:

output_dir = carb.tokens.get_tokens_interface().resolve("${test_output}")

When running on CI this folder becomes a build artifact.

Python debugger

To enable python debugger you can use omni.kit.debug.python extension. One way is to uncomment in omni.app.test_ext.kit:

    # "omni.kit.debug.python" = {}

You can use VSCode to attach a python debugger. Look into omni.kit.debug.python extension.toml for more settings, and check the FAQ section for a walkthrough.

Wait for the debugger to attach

If you want to attach a debugger, you can run with the -d flag. When Kit runs with -d, it stops and wait for debugger to attach, which can also can be skipped. Since we run 2 processes, you likely want to attach to the second one - skip the first one. E.g.:

λ _build\windows-x86_64\release\tests-example.python_ext.bat -d
[omni.kit.app] Waiting for debugger to attach, press any key to skip... [pid: 19052]
[Info] [carb] Logging to file: C:/projects/extensions/kit-template/_build/windows-x86_64/release//logs/Kit/kit/103.0/kit_20211018_160436.log
Test output path: C:\projects\extensions\kit-template\_testoutput
Running 1 Extension Test(s).

||||||||||||||||||||||||||||||  [EXTENSION TEST START: example.python_ext-0.2.1]  ||||||||||||||||||||||||||||||
>>> running process: C:\projects\extensions\kit-template\_build\windows-x86_64\release\kit\kit.exe ${kit}/apps/omni.app.test_ext.kit --enable example.python_ext-0.2.1 --/log/flushStandardStreamOutput=1 --/app/name=exttest_example.python_ext-0.2.1 --/log/file='C:\projects\extensions\kit-template\_testoutput/exttest_example.python_ext-0.2.1/exttest_example.python_ext-0.2.1_2021-10-18T16-04-37.log' --/crashreporter/dumpDir='C:\projects\extensions\kit-template\_testoutput/exttest_example.python_ext-0.2.1' --/plugins/carb.profiler-cpu.plugin/saveProfile=1 --/plugins/carb.profiler-cpu.plugin/compressProfile=1 --/app/profileFromStart=1 --/plugins/carb.profiler-cpu.plugin/filePath='C:\projects\extensions\kit-template\_testoutput/exttest_example.python_ext-0.2.1/ct_exttest_example.python_ext-0.2.1_2021-10-18T16-04-37.gz' --ext-folder c:/projects/extensions/kit-template/_build/windows-x86_64/release/kit/extsPhysics --ext-folder c:/projects/extensions/kit-converters/_build/windows-x86_64/release/exts --ext-folder C:/projects/extensions/kit-template/_build/windows-x86_64/release/exts --ext-folder C:/projects/extensions/kit-template/_build/windows-x86_64/release/apps --enable omni.kit.test --/exts/omni.kit.test/runTestsAndQuit=true --/exts/omni.kit.test/includeTests/0='example.python_ext.*' --portable-root C:\projects\extensions\kit-template\_build\windows-x86_64\release\/ -d
|| [omni.kit.app] Waiting for debugger to attach, press any key to skip... [pid: 22940]

Alternatively, pass -d directly to the second process by putting it after --:

_build\windows-x86_64\release\tests-[extension_name].bat -- -d

Reading Logs

Each process writes own log file. Paths to those files are printed to stdout. You can run with -v to increase the verbosity of standard output.

Run from Extension Manager

You can also run tests from UI. Run any Kit with UI, for instance omni.app.mini.kit. Go to Extension Manager, find your extension, open Tests tab. Here you can run the same tests.

It will also run a separate process and works exactly the same way as running from the shell script.

Marking tests as unreliable

It is often the case that certain tests can fail randomly, with some probability. That can block CI/CD pipelines and lowers the trust into the TC state.

In that case:

  1. Create a ticket with Kit:UnreliableTests label

  2. Mark a test as unreliable and leave the ticket number in the comment

Unreliable tests do not run as part of the regular CI pipeline. They run in the separate nightly TC job.

There are 2 ways to mark a test as unreliable:

  1. Mark whole test process as unreliable:

unreliable = true
  1. Mark specific python tests as unreliable:

pythonTests.unreliable = [ "*test_name" ]

Running unreliable tests

To run unreliable tests (and only them) pass --/exts/omni.kit.test/testExtRunUnreliableTests=1 to the test runner:

> _build\windows-x86_64\release\tests-example.python_ext.bat --/exts/omni.kit.test/testExtRunUnreliableTests=1

Listing tests

To list tests without running, pass --/exts/omni.kit.test/printTestsAndQuit=1. That will still take some time to start the tested extension. It is a limitation of the testing system that it can’t find tests without setting up python environment:

> _build\windows-x86_64\release\tests-example.python_ext.bat --/exts/omni.kit.test/printTestsAndQuit=1

Look for lines like:

|| ========================================
|| Printing All Tests (count: 6):
|| ========================================
|| omni.kit.commands.tests.test_commands.TestCommands.test_callbacks
|| omni.kit.commands.tests.test_commands.TestCommands.test_command_parameters
|| omni.kit.commands.tests.test_commands.TestCommands.test_commands
|| omni.kit.commands.tests.test_commands.TestCommands.test_error
|| omni.kit.commands.tests.test_commands.TestCommands.test_group
|| omni.kit.commands.tests.test_commands.TestCommands.test_multiple_calls

Accordingly, to list unreliable tests add --/exts/omni.kit.test/testExtRunUnreliableTests=1:

> _build\windows-x86_64\release\tests-example.python_ext.bat --/exts/omni.kit.test/testExtRunUnreliableTests=1 --/exts/omni.kit.test/printTestsAndQuit=1

repo_test: Running All Tests

To run all tests in the repo we use repo_test repo tool. Which is yet another process that runs before anything. It globs all the files according to repo.toml [repo_test] section configuration and runs them.

It is one entry point to run all sorts of tests. Different kinds of tests are grouped into suites. By default, it will run one suite, but you can select which suite to run with --suite [suite name]. Look at repo.toml for entries like [repo_test.suites.pythontests]. In that example: pythontests is a suite name.

You can also choose a build config to run tests on: -c release or -c debug. In kit the default is debug, in other repos: release.

Run all tests in the repo:

> repo.bat test


> repo.bat test --suite pythontests -c release

Just print them:

> repo.bat test -l

To filter tests:

> repo.bat test -f foobar

For more options (as usual):

> repo.bat test -h

Excluding Tests from TC:

You can control which shell scripts to run with repo_test in repo.toml:

# Run all test
include = [
exclude = [
  "tests-example.cpp_ext*", # Exclude some script
args = []

Check before running with:

> repo.bat test -l

Adding Info to Failed Test Summary

If a test fails, a summary is printed to stdout that looks like so:

[fail] Extension Test failed. Details:
    Cmd: kit.exe ...
    Return code: 13
    Failure reasons:
        Process return code: 13 != 0.
    Failing tests: ['test_all (omni.example.ui.tests.example_ui_test.TestExampleUi)']

You can add more fields to this summary by printing special pragmas to stdout from your tests (in fact, the Failing tests field above is done this way). For example, if you were to add the line print("##omni.kit.test[set, foo, bah]") to the test above, then the summary would look like so:

[fail] Extension Test failed. Details:
    Cmd: kit.exe ...
    Return code: 13
    Failure reasons:
        Process return code: 13 != 0.
    Failing tests: ['test_all (omni.example.ui.tests.example_ui_test.TestExampleUi)']
    foo: bah

Pragma operations must appear at the start of a line. They should appear on their own, and any further pragmas on the same line will be ignored.

Available pragma operations are:

  • set: Set a field. Example: ##omni.kit.test[set, foo, bah]

  • append: Append to a list field. Example: ##omni.kit.test[append, foo, bah]

Note that if a pragma fails for any reason (the syntax is incorrect; you try to append to a value that was previously set), it will be silently ignored.

omni.kit.ui_test: Writing UI tests

Many extensions build various windows and widgets using omni.ui. The best way to test them is by simulating user interactions with the UI. For that omni.kit.ui_test extension can be used.

omni.kit.ui_test provides a way to query UI elements and interact with them. To start add test dependency to this extension:

dependencies = [

Now you can import and use it in tests. Example:

import omni.kit.ui_test as ui_test

async def test_button(self):
    # Find a button
    button = ui_test.find("Nice Window//Frame/**/Button[*]")

    # button is a reference, actual omni.ui.Widget can be accessed:
    print(type(button.widget))  # <class 'omni.ui._ui.Button'>

    # Click on button
    await button.click())

Refer to omni.kit.ui_test documentation for more examples and API.

(Advanced) Generating new tests or adapting discovered tests at runtime

Python unit tests are discovered at runtime. We introduced a way to adapt and/or extend the list of tests by implementing custom omni.kit.test.AsyncTestCase class with def generate_extra_tests(self) method.

This method allows:

  • changes to discovered test case by mutating self instance

  • generation of new test cases by returning a list of them

In general, this method is preferred when same set of tests needs to be validated with multiple different configurations. For example, when developing new subsystems while maintaining the old ones.