def METHOD_NAME(create_command, first_app_config, capsys):
    """If the system python doesn't match the target python, a warning is raised."""
    first_app_config.python_version_tag = "3"
    first_app_config.target_image = "somevendor:surprising"
    create_command.tools[first_app_config].app_context = DockerAppContext(
        tools=create_command.tools,
        app=first_app_config,
    )
    # Mock a return value from Docker that matches the system Python
    create_command.tools[first_app_config].app_context.check_output = MagicMock(
        return_value="3.42\n"
    )
    # Verify python for the app
    create_command.verify_python(first_app_config)
    # The docker container was interrogated for a Python version
    create_command.tools[
        first_app_config
    ].app_context.check_output.assert_called_once_with(
        [
            "python3",
            "-c",
            (
                "import sys; "
                "print(f'{sys.version_info.major}.{sys.version_info.minor}')"
            ),
        ]
    )
    # Warning message was recorded
    assert "WARNING: Python version mismatch!" in capsys.readouterr().out
    # The python version has been updated
    assert first_app_config.python_version_tag == "3.42"