# 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 whichever effort goes into ensuring backward 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

- tempest.common.credentials_factory

- tempest.clients

- tempest.test

- tempest.scenario.manager

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://opendev.org/openstack/tempest-plugin-cookiecutter.git

    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 mandatory methods in the abstract class, you can refer to the api doc below for a reference of what that entails.

### Abstract Plugin Class

class TempestPlugin

  Provide basic hooks for an external plugin

  To provide tempest the necessary information to run the plugin.

## Plugin Structure

While there are no hard and fast rules for the structure of 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.

### Service Clients

If a plugin defines a service client, it is beneficial for it to implement the `get_service_clients` method in the plugin class. All service clients which are exposed via this interface will be automatically configured and be available in any instance of the service clients class, defined in `tempest.lib.services.clients.ServiceClients`. In case multiple plugins are installed, all service clients from all plugins will be registered, making it easy to write tests which rely on multiple APIs whose service clients are in different plugins.

Example implementation of `get_service_clients`:

    def get_service_clients(self):
        # Example implementation with two service clients
        my_service1_config = config.service_client_config('my_service')
        params_my_service1 = {
            'name': 'my_service_v1',
            'service_version': 'my_service.v1',
            'module_path': 'plugin_tempest_tests.services.my_service.v1',
            'client_names': ['API1Client', 'API2Client'],
        }
        params_my_service1.update(my_service_config)
        my_service2_config = config.service_client_config('my_service')
        params_my_service2 = {
            'name': 'my_service_v2',
            'service_version': 'my_service.v2',
            'module_path': 'plugin_tempest_tests.services.my_service.v2',
            'client_names': ['API1Client', 'API2Client'],
        }
        params_my_service2.update(my_service2_config)
        return [params_my_service1, params_my_service2]

Parameters:

- name: Name of the attribute used to access the `ClientsFactory` from the `ServiceClients` instance. See example below.

- service_version: Tempest enforces a single implementation for each service client. Available service clients are held in a `ClientsRegistry` singleton, and registered with `service_version`, which means that `service_version` must be unique and it should represent the service API and version implemented by the service client.

- module_path: Relative to the service client module, from the root of the plugin.

- client_names: Name of the classes that implement service clients in the service clients module.

Example usage of the service clients in tests:

    # my_creds is instance of tempest.lib.auth.Credentials
    # identity_uri is v2 or v3 depending on the configuration
    from tempest.lib.services import clients

    my_clients = clients.ServiceClients(my_creds, identity_uri)
    my_service1_api1_client = my_clients.my_service_v1.API1Client()
    my_service2_api1_client = my_clients.my_service_v2.API1Client(my_args='any')

Automatic configuration and registration of service clients imposes some extra constraints on the structure of the configuration options exposed by the plugin.

First `service_version` should be in the format service_config[.version]. The .version part is optional, and should only be used if there are multiple versions of the same API available. The service_config must match the name of a configuration options group defined by the plugin. Different versions of one API must share the same configuration group.

Second the configuration options group service_config must contain the following options:

- catalog_type: corresponds to service in the catalog

- endpoint_type

The following options will be honoured if defined, but they are not mandatory, as they do not necessarily apply to all service clients.

- region: default to identity.region

- build_timeout : default to compute.build_timeout

- build_interval: default to compute.build_interval

Third the service client classes should inherit from `RestClient`, should accept generic keyword arguments, and should pass those arguments to the `__init__` method of `RestClient`. Extra arguments can be added. For instance:

    class MyAPIClient(rest_client.RestClient):

        def __init__(self, auth_provider, service, region,
                     my_arg, my_arg2=True, **kwargs):
            super(MyAPIClient, self).__init__(
                auth_provider, service, region, **kwargs)
            self.my_arg = my_arg
            self.my_args2 = my_arg

Finally the service client should be structured in a python module, so that all service client classes are importable from it. Each major API version should have its own module.

The following folder and module structure is recommended for a single major API version:

    plugin_dir/
      services/
        __init__.py
        client_api_1.py
        client_api_2.py

The content of __init__.py module should be:

    from client_api_1.py import API1Client
    from client_api_2.py import API2Client

    __all__ = ['API1Client', 'API2Client']

The following folder and module structure is recommended for multiple major API version:

    plugin_dir/
      services/
        v1/
           __init__.py
           client_api_1.py
           client_api_2.py
        v2/
           __init__.py
           client_api_1.py
           client_api_2.py

The content each of __init__.py module under vN should be:

    from client_api_1.py import API1Client
    from client_api_2.py import API2Client

    __all__ = ['API1Client', 'API2Client']

## 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.

this page last updated: 2022-01-10 15:51:28

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