tempest/doc/source/plugin.rst

Tempest Test Plugin Interface

Tempest has an external test plugin interface which enables anyone to integrate an external test suite as part of a tempest run. This will let any project leverage being run with the rest of the tempest suite while not requiring the tests live in the tempest tree.

Creating a plugin

Creating a plugin is fairly straightforward and doesn't require much additional effort on top of creating a test suite using tempest.lib. One thing to note with doing this is that the interfaces exposed by tempest are not considered stable (with the exception of configuration variables which ever effort goes into ensuring backwards compatibility). You should not need to import anything from tempest itself except where explicitly noted.

Stable Tempest APIs plugins may use

As noted above, several tempest APIs are acceptable to use from plugins, while others are not. A list of stable APIs available to plugins is provided below:

• tempest.lib.*
• tempest.config
• tempest.test_discover.plugins

If there is an interface from tempest that you need to rely on in your plugin which is not listed above, it likely needs to be migrated to tempest.lib. In that situation, file a bug, push a migration patch, etc. to expedite providing the interface in a reliable manner.

Plugin Cookiecutter

In order to create the basic structure with base classes and test directories you can use the tempest-plugin-cookiecutter project:

> pip install -U cookiecutter && cookiecutter https://git.openstack.org/openstack/tempest-plugin-cookiecutter

Cloning into 'tempest-plugin-cookiecutter'...
remote: Counting objects: 17, done.
remote: Compressing objects: 100% (13/13), done.
remote: Total 17 (delta 1), reused 14 (delta 1)
Unpacking objects: 100% (17/17), done.
Checking connectivity... done.
project (default is "sample")? foo
testclass (default is "SampleTempestPlugin")? FooTempestPlugin

This would create a folder called foo_tempest_plugin/ with all necessary basic classes. You only need to move/create your test in foo_tempest_plugin/tests.

Entry Point

Once you've created your plugin class you need to add an entry point to your project to enable tempest to find the plugin. The entry point must be added to the "tempest.test_plugins" namespace.

If you are using pbr this is fairly straightforward, in the setup.cfg just add something like the following:

[entry_points]
tempest.test_plugins =
    plugin_name = module.path:PluginClass

Standalone Plugin vs In-repo Plugin

Since all that's required for a plugin to be detected by tempest is a valid setuptools entry point in the proper namespace there is no difference from the tempest perspective on either creating a separate python package to house the plugin or adding the code to an existing python project. However, there are tradeoffs to consider when deciding which approach to take when creating a new plugin.

If you create a separate python project for your plugin this makes a lot of things much easier. Firstly it makes packaging and versioning much simpler, you can easily decouple the requirements for the plugin from the requirements for the other project. It lets you version the plugin independently and maintain a single version of the test code across project release boundaries (see the Branchless Tempest Spec for more details on this). It also greatly simplifies the install time story for external users. Instead of having to install the right version of a project in the same python namespace as tempest they simply need to pip install the plugin in that namespace. It also means that users don't have to worry about inadvertently installing a tempest plugin when they install another package.

The sole advantage to integrating a plugin into an existing python project is that it enables you to land code changes at the same time you land test changes in the plugin. This reduces some of the burden on contributors by not having to land 2 changes to add a new API feature and then test it and doing it as a single combined commit.

Plugin Class

To provide tempest with all the required information it needs to be able to run your plugin you need to create a plugin class which tempest will load and call to get information when it needs. To simplify creating this tempest provides an abstract class that should be used as the parent for your plugin. To use this you would do something like the following:

from tempest.test_discover import plugins

class MyPlugin(plugins.TempestPlugin):

Then you need to ensure you locally define all of the methods in the abstract class, you can refer to the api doc below for a reference of what that entails.

Abstract Plugin Class

tempest.test_discover.plugins.TempestPlugin

Plugin Structure

While there are no hard and fast rules for the structure a plugin, there are basically no constraints on what the plugin looks like as long as the 2 steps above are done. However, there are some recommended patterns to follow to make it easy for people to contribute and work with your plugin. For example, if you create a directory structure with something like:

plugin_dir/
  config.py
  plugin.py
  tests/
    api/
    scenario/
  services/
    client.py

That will mirror what people expect from tempest. The file

• config.py: contains any plugin specific configuration variables
• plugin.py: contains the plugin class used for the entry point

• tests: the directory where test discovery will be run, all tests should

  be under this dir

• services: where the plugin specific service clients are

Additionally, when you're creating the plugin you likely want to follow all of the tempest developer and reviewer documentation to ensure that the tests being added in the plugin act and behave like the rest of tempest.

Dealing with configuration options

Historically Tempest didn't provide external guarantees on its configuration options. However, with the introduction of the plugin interface this is no longer the case. An external plugin can rely on using any configuration option coming from Tempest, there will be at least a full deprecation cycle for any option before it's removed. However, just the options provided by Tempest may not be sufficient for the plugin. If you need to add any plugin specific configuration options you should use the register_opts and get_opt_lists methods to pass them to Tempest when the plugin is loaded. When adding configuration options the register_opts method gets passed the CONF object from tempest. This enables the plugin to add options to both existing sections and also create new configuration sections for new options.

Using Plugins

Tempest will automatically discover any installed plugins when it is run. So by just installing the python packages which contain your plugin you'll be using them with tempest, nothing else is really required.

However, you should take care when installing plugins. By their very nature there are no guarantees when running tempest with plugins enabled about the quality of the plugin. Additionally, while there is no limitation on running with multiple plugins it's worth noting that poorly written plugins might not properly isolate their tests which could cause unexpected cross interactions between plugins.

Notes for using plugins with virtualenvs

When using a tempest inside a virtualenv (like when running under tox) you have to ensure that the package that contains your plugin is either installed in the venv too or that you have system site-packages enabled. The virtualenv will isolate the tempest install from the rest of your system so just installing the plugin package on your system and then running tempest inside a venv will not work.

Tempest also exposes a tox job, all-plugin, which will setup a tox virtualenv with system site-packages enabled. This will let you leverage tox without requiring to manually install plugins in the tox venv before running tests.