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Writing Basic Tests with Python

Starting point: we’ll assume you have a basic ament_python package set up already and you want to add some tests to it.

If you are using ament_cmake_python, refer to the the ament_cmake_python docs for how to make tests dicoverable. The test contents and invocation with colcon remain the same.

Package Setup

setup.py

Your setup.py must a test dependency on pytest within the call to setup(...):

tests_require=['pytest'],

Test Files and Folders

Your test code needs to go in a folder named tests in the root of your package.

Any file that contains tests that you want to run must have the pattern test_FOO.py where FOO can be replaced with anything.

Example package layout:

awesome_ros_package/
  awesome_ros_package/
      __init__.py
      fozzie.py
  package.xml
  setup.cfg
  setup.py
  tests/
      test_init.py
      test_copyright.py
      test_fozzie.py

Test Contents

You can now write tests to your heart’s content. There are plenty of resources on pytest, but in short, you can write functions with the test_ prefix and include whatever assert statements you’d like.

def test_math():
    assert 2 + 2 == 5   # This should fail for most mathematical systems

Special Commands

Beyond the standard colcon testing commands you can also specify arguments to the pytest framework from the command line with the --pytest-args flag. For example, you can specify the name of the function to run with

colcon test --packages-select <name-of-pkg> --pytest-args -k name_of_the_test_function