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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. If there is an interface from tempest that you need to rely on in your plugin 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 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 plugin

class MyPlugin(plugin.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.

Also, note eventually this abstract class will likely live in tempest-lib, when that migration occurs a deprecation shim will be added to tempest so as to not break any existing plugins. But, when that occurs migrating to using tempest-lib as the source for the abstract class will be prudent.

Abstract Plugin Class

tempest.test_discover.plugins.TempestPlugin

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

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.

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