Test parameters


This section describes in detail what test parameters are and how the whole variants mechanism works in Avocado. If you’re interested in the basics, see Accessing test parameters or practical view by examples in YAML to Mux plugin.

Avocado allows passing parameters to tests, which effectively results in several different variants of each test. These parameters are available in (test’s) self.params and are of avocado.core.parameters.AvocadoParams type. You can also access these parameters via the configuration dict at run.test_parameters namespace.

The data for self.params are supplied by avocado.core.varianter.Varianter which asks all registered plugins for variants or uses default when no variants are defined.

Overall picture of how the params handling works is:

    |           |  // Test uses AvocadoParams, with content either from
    |   Test    |  // a variant or from the test parameters given by
    |           |  // "--test-parameter"
    |  Runner   |  // iterates through tests and variants to run all
    +-----^-----+  // desired combinations specified by "--execution-order".
          |        // if no variants are produced by varianter plugins,
          |        // use the test parameters given by "--test-parameter"
+-------------------+ provide variants +-----------------------+
|                   |<-----------------|                       |
| Varianter API     |                  | Varianter plugins API |
|                   |                  |                       |
+-------------------+                  +-----------------------+
                                           |  // All plugins are invoked
                                           |  // in turns
              |                                  |
              |                                  |
              v                                  v
    +--------------------+           +-------------------------+
    | yaml_to_mux plugin |           | Other variant plugin(s) |
    +-----^--------------+           +-------------------------+
          |  // yaml is parsed to MuxTree,
          |  // multiplexed and yields variants
    | +------------+ +--------------+ |
    | | --mux-yaml | | --mux-inject | |
    | +------------+ +--------------+ |

Let’s introduce the basic keywords.



Is a node object allowing to create tree-like structures with parent->multiple_children relations and storing params. It can also report it’s environment, which is set of params gathered from root to this node. This is used in tests where instead of passing the full tree only the leaf nodes are passed and their environment represents all the values of the tree.



Is a “database” of params present in every (instrumented) Avocado test. It’s produced during avocado.core.test.Test’s __init__ from a variant. It accepts a list of TreeNode objects; test name avocado.core.test_id.TestID (for logging purposes) and a list of default paths (Parameter Paths).

In test it allows querying for data by using:

self.params.get($name, $path=None, $default=None)


  • name - name of the parameter (key)

  • path - where to look for this parameter (when not specified uses mux-path)

  • default - what to return when param not found

Each variant defines a hierarchy, which is preserved so AvocadoParams follows it to return the most appropriate value or raise Exception on error.

Parameter Paths

As test params are organized in trees, it’s possible to have the same variant in several locations. When they are produced from the same TreeNode, it’s not a problem, but when they are a different values there is no way to distinguish which should be reported. One way is to use specific paths, when asking for params, but sometimes, usually when combining upstream and downstream variants, we want to get our values first and fall-back to the upstream ones when they are not found.

For example let’s say we have upstream values in /upstream/sleeptest and our values in /downstream/sleeptest. If we asked for a value using path "*", it’d raise an exception being unable to distinguish whether we want the value from /downstream or /upstream. We can set the parameter paths to ["/downstream/*", "/upstream/*"] to make all relative calls (path starting with *) to first look in nodes in /downstream and if not found look into /upstream.

More practical overview of parameter paths is in YAML to Mux plugin in Resolution order section.


Variant is a set of params produced by Varianter and passed to the test by the test runner as params argument. The simplest variant is None, which still produces an empty AvocadoParams. Also, the Variant can also be a tuple(list, paths) or just the list of avocado.core.tree.TreeNode with the params.

Dumping/Loading Variants

Depending on the number of parameters, generating the Variants can be very compute intensive. As the Variants are generated as part of the Job execution, that compute intensive task will be executed by the systems under test, causing a possibly unwanted cpu load on those systems.

To avoid such situation, you can acquire the resulting JSON serialized variants file, generated out of the variants computation, and load that file on the system where the Job will be executed.

There are two ways to acquire the JSON serialized variants file:

  • Using the --json-variants-dump option of the avocado variants command:

    $ avocado variants --mux-yaml examples/yaml_to_mux/hw/hw.yaml --json-variants-dump variants.json
    $ file variants.json
    variants.json: ASCII text, with very long lines, with no line terminators
  • Getting the auto-generated JSON serialized variants file after a Avocado Job execution (named with a numeric index for each of the job’s suites):

    $ avocado run examples/tests/passtest.py --mux-yaml examples/yaml_to_mux/hw/hw.yaml
    $ file $HOME/avocado/job-results/latest/jobdata/variants-1.json
    $HOME/avocado/job-results/latest/jobdata/variants.json: ASCII text, with very long lines, with no line terminators

Once you have the variants.json file, you can load it on the system where the Job will take place:

$ avocado run examples/tests/passtest.py --json-variants-load variants.json
JOB ID     : f2022736b5b89d7f4cf62353d3fb4d7e3a06f075
JOB LOG    : $HOME/avocado/job-results/job-2018-02-09T14.39-f202273/job.log
   (1/6) examples/tests/passtest.py:PassTest.test;run-cpu-intel-disk-scsi-d340: STARTED
   (1/6) examples/tests/passtest.py:PassTest.test;run-cpu-intel-disk-scsi-d340: PASS (0.01 s)
   (2/6) examples/tests/passtest.py:PassTest.test;run-cpu-intel-disk-virtio-40ba: STARTED
   (2/6) examples/tests/passtest.py:PassTest.test;run-cpu-intel-disk-virtio-40ba: PASS (0.01 s)
   (3/6) examples/tests/passtest.py:PassTest.test;run-cpu-amd-disk-scsi-b3e2: STARTED
   (3/6) examples/tests/passtest.py:PassTest.test;run-cpu-amd-disk-scsi-b3e2: PASS (0.01 s)
   (4/6) examples/tests/passtest.py:PassTest.test;run-cpu-amd-disk-virtio-9d9f: STARTED
   (4/6) examples/tests/passtest.py:PassTest.test;run-cpu-amd-disk-virtio-9d9f: PASS (0.01 s)
   (5/6) examples/tests/passtest.py:PassTest.test;run-cpu-arm-disk-scsi-0ceb: STARTED
   (5/6) examples/tests/passtest.py:PassTest.test;run-cpu-arm-disk-scsi-0ceb: PASS (0.01 s)
   (6/6) examples/tests/passtest.py:PassTest.test;run-cpu-arm-disk-virtio-0254: STARTED
   (6/6) examples/tests/passtest.py:PassTest.test;run-cpu-arm-disk-virtio-0254: PASS (0.01 s)
JOB TIME   : 0.51 s
JOB HTML   : $HOME/avocado/job-results/job-2018-02-09T14.39-f202273/results.html



Is an internal object which is used to interact with the variants mechanism in Avocado. It’s lifecycle is compound of two stages. First it allows the core/plugins to inject default values, then it is parsed and only allows querying for values, number of variants and such.

Example workflow of avocado run passtest.py -m example.yaml is:

avocado run examples/tests/passtest.py -m example.yaml
  + parser.finish -> Varianter.__init__  // dispatcher initializes all plugins
  + job.run_tests -> Varianter.is_parsed
  + job.run_tests -> Varianter.parse
  |                     // processes default params
  |                     // initializes the plugins
  |                     // updates the default values
  + job._log_variants -> Varianter.to_str  // prints the human readable representation to log
  + runner.run_suite -> Varianter.get_number_of_tests
  + runner._iter_variants -> Varianter.itertests  // Yields variants

The Varianter itself can only produce an empty variant, but it invokes all Varianter plugins and if any of them reports variants it yields them instead of the default variant.

Test parameters

This is an Avocado core feature, that is, it’s not dependent on any varianter plugin. In fact, it’s only active when no Varianter plugin is used and produces a valid variant.

Avocado will use those simple parameters, and will pass them to all tests in a job execution. This is done on the command line via --test-parameter, or simply, -p. It can be given multiple times for multiple parameters.

Because Avocado parameters do not have a mechanism to define their types, test code should always consider that a parameter value is a string, and convert it to the appropriate type.


Some varianter plugins would implicitly set parameters with different data types, but given that the same test can be used with different, or none, varianter plugins, it’s safer if the test does an explicit check or type conversion.

Because the avocado.core.parameters.AvocadoParams mandates the concept of a parameter path (a legacy of the tree based Multiplexer) and these test parameters are flat, those test parameters are placed in the / path. This is to ensure maximum compatibility with tests that do not choose an specific parameter location.

Varianter plugins


A plugin interface that can be used to build custom plugins which are used by Varianter to get test variants. For inspiration see avocado_varianter_yaml_to_mux.YamlToMux which is an optional varianter plugin. Details about this plugin can be found here YAML to Mux plugin.