Setting Up a Development Environment

This page describes how to setup a working Python development environment that can be used in developing Neutron on Ubuntu, Fedora or Mac OS X. These instructions assume you’re already familiar with Git and Gerrit, which is a code repository mirror and code review toolset , however if you aren’t please see this Git tutorial for an introduction to using Git and this guide for a tutorial on using Gerrit and Git for code contribution to Openstack projects.

Following these instructions will allow you to run the Neutron unit tests. If you want to be able to run Neutron in a full OpenStack environment, you can use the excellent DevStack project to do so. There is a wiki page that describes setting up Neutron using DevStack.

Getting the code

Grab the code:

git clone git://
cd neutron

Testing Neutron


Neutron relies on unit, functional, fullstack and API tests to ensure its quality, as described below. In addition to in-tree testing, Tempest is responsible for validating Neutron’s integration with other OpenStack components via scenario tests, and Rally is responsible for benchmarking.

Unit Tests

Unit tests (neutron/test/unit/) are meant to cover as much code as possible. They are designed to test the various pieces of the Neutron tree to make sure any new changes don’t break existing functionality. Unit tests have no requirements nor make changes to the system they are running on. They use an in-memory sqlite database to test DB interaction.

Functional Tests

Functional tests (neutron/tests/functional/) are intended to validate actual system interaction. Mocks should be used sparingly, if at all. Care should be taken to ensure that existing system resources are not modified and that resources created in tests are properly cleaned up both on test success and failure.

Fullstack Tests

Fullstack tests (neutron/tests/fullstack/) target Neutron as a whole. The test infrastructure itself manages the Neutron server and its agents. Fullstack tests are a form of integration testing and fill a void between unit/functional tests and Tempest. More information may be found here.

API Tests

API tests (neutron/tests/api/) are intended to ensure the function and stability of the Neutron API. As much as possible, changes to this path should not be made at the same time as changes to the code to limit the potential for introducing backwards-incompatible changes, although the same patch that introduces a new API should include an API test.

Since API tests target a deployed Neutron daemon that is not test-managed, they should not depend on controlling the runtime configuration of the target daemon. API tests should be black-box - no assumptions should be made about implementation. Only the contract defined by Neutron’s REST API should be validated, and all interaction with the daemon should be via a REST client.

neutron/tests/api was copied from the Tempest project. The Tempest networking API directory was frozen and any new tests belong to the Neutron repository.

Development Process

It is expected that any new changes that are proposed for merge come with tests for that feature or code area. Ideally any bugs fixes that are submitted also have tests to prove that they stay fixed! In addition, before proposing for merge, all of the current tests should be passing.

Structure of the Unit Test Tree

The structure of the unit test tree should match the structure of the code tree, e.g.

- target module: neutron.agent.utils

- test module: neutron.tests.unit.agent.test_utils

Unit test modules should have the same path under neutron/tests/unit/ as the module they target has under neutron/, and their name should be the name of the target module prefixed by test_. This requirement is intended to make it easier for developers to find the unit tests for a given module.

Similarly, when a test module targets a package, that module’s name should be the name of the package prefixed by test_ with the same path as when a test targets a module, e.g.

- target package: neutron.ipam

- test module: neutron.tests.unit.test_ipam

The following command can be used to validate whether the unit test tree is structured according to the above requirements:


Where appropriate, exceptions can be added to the above script. If code is not part of the Neutron namespace, for example, it’s probably reasonable to exclude their unit tests from the check.

Running Tests

There are three mechanisms for running tests:, tox, and nose2. Before submitting a patch for review you should always ensure all test pass; a tox run is triggered by the jenkins gate executed on gerrit for each patch pushed for review.

With these mechanisms you can either run the tests in the standard environment or create a virtual environment to run them in.

By default after running all of the tests, any pep8 errors found in the tree will be reported.


You can use the script in the root source directory to execute tests in a virtualenv:

./run_tests -V

With nose2

You can use nose2 to run individual tests, as well as use for debugging portions of your code:

source .venv/bin/activate
pip install nose2

There are disadvantages to running nose2 - the tests are run sequentially, so race condition bugs will not be triggered, and the full test suite will take significantly longer than tox & testr. The upside is that testr has some rough edges when it comes to diagnosing errors and failures, and there is no easy way to set a breakpoint in the Neutron code, and enter an interactive debugging session while using testr.

Note that nose2’s predecessor, nose, does not understand load_tests protocol introduced in Python 2.7. This limitation will result in errors being reported for modules that depend on load_tests (usually due to use of testscenarios). nose, therefore, is not supported, while nose2 is.

With tox

Neutron, like other OpenStack projects, uses tox for managing the virtual environments for running test cases. It uses Testr for managing the running of the test cases.

Tox handles the creation of a series of virtualenvs that target specific versions of Python.

Testr handles the parallel execution of series of test cases as well as the tracking of long-running tests and other things.

For more information on the standard Tox-based test infrastructure used by OpenStack and how to do some common test/debugging procedures with Testr, see this wiki page:

PEP8 and Unit Tests

Running pep8 and unit tests is as easy as executing this in the root directory of the Neutron source code:


To run only pep8:

tox -e pep8

Since pep8 includes running pylint on all files, it can take quite some time to run. To restrict the pylint check to only the files altered by the latest patch changes:

tox -e pep8 HEAD~1

To run only the unit tests:

tox -e py27

Functional Tests

To run functional tests that do not require sudo privileges or specific-system dependencies:

tox -e functional

To run all the functional tests, including those requiring sudo privileges and system-specific dependencies, the procedure defined by tools/ should be followed.

IMPORTANT: relies on DevStack to perform extensive modification to the underlying host. Execution of the script requires sudo privileges and it is recommended that the following commands be invoked only on a clean and disposeable VM. A VM that has had DevStack previously installed on it is also fine.

git clone ../devstack
./tools/ ../devstack -i
tox -e dsvm-functional

The ‘-i’ option is optional and instructs the script to use DevStack to install and configure all of Neutron’s package dependencies. It is not necessary to provide this option if DevStack has already been used to deploy Neutron to the target host.

Fullstack Tests

To run all the full-stack tests, you may use:

tox -e dsvm-fullstack

Since full-stack tests often require the same resources and dependencies as the functional tests, using the configuration script tools/ is advised (As described above). When running full-stack tests on a clean VM for the first time, we advise to run ./ successfully to make sure all Neutron’s dependencies are met. Full-stack based Neutron daemons produce logs to a sub-folder in /tmp/fullstack-logs (for example, a test named “test_example” will produce logs to /tmp/fullstack-logs/test_example/), so that will be a good place to look if your test is failing.

API Tests

To run the api tests, deploy Tempest and Neutron with DevStack and then run the following command:

tox -e api

If tempest.conf cannot be found at the default location used by DevStack (/opt/stack/tempest/etc) it may be necessary to set TEMPEST_CONFIG_DIR before invoking tox:

export TEMPEST_CONFIG_DIR=[path to dir containing tempest.conf]
tox -e api

Running Individual Tests

For running individual test modules, cases or tests, you just need to pass the dot-separated path you want as an argument to it.

For example, the following would run only a single test or test case:

$ ./ neutron.tests.unit.test_manager
$ ./ neutron.tests.unit.test_manager.NeutronManagerTestCase
$ ./ neutron.tests.unit.test_manager.NeutronManagerTestCase.test_service_plugin_is_loaded


$ tox -e py27 neutron.tests.unit.test_manager
$ tox -e py27 neutron.tests.unit.test_manager.NeutronManagerTestCase
$ tox -e py27 neutron.tests.unit.test_manager.NeutronManagerTestCase.test_service_plugin_is_loaded


Neutron has a fast growing code base and there are plenty of areas that need better coverage.

To get a grasp of the areas where tests are needed, you can check current unit tests coverage by running:

$ ./ -c

Since the coverage command can only show unit test coverage, a coverage document is maintained that shows test coverage per area of code in: doc/source/devref/testing_coverage.rst.


By default, calls to pdb.set_trace() will be ignored when tests are run. For pdb statements to work, invoke run_tests as follows:

$ ./ -d [test module path]

It’s possible to debug tests in a tox environment:

$ tox -e venv -- python -m [test module path]

Tox-created virtual environments (venv’s) can also be activated after a tox run and reused for debugging:

$ tox -e venv
$ . .tox/venv/bin/activate
$ python -m [test module path]

Tox packages and installs the Neutron source tree in a given venv on every invocation, but if modifications need to be made between invocation (e.g. adding more pdb statements), it is recommended that the source tree be installed in the venv in editable mode:

# run this only after activating the venv
$ pip install --editable .

Editable mode ensures that changes made to the source tree are automatically reflected in the venv, and that such changes are not overwritten during the next tox run.

Post-mortem Debugging

Setting OS_POST_MORTEM_DEBUGGER in the shell environment will ensure that the debugger .post_mortem() method will be invoked on test failure:

$ OS_POST_MORTEM_DEBUGGER=pdb ./ -d [test module path]

Supported debuggers are pdb, and pudb. Pudb is full-screen, console-based visual debugger for Python which let you inspect variables, the stack, and breakpoints in a very visual way, keeping a high degree of compatibility with pdb:

$ ./.venv/bin/pip install pudb

$ OS_POST_MORTEM_DEBUGGER=pudb ./ -d [test module path]


[1]PUDB debugger: