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
self.params and are of
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-parameters" +-----^-----+ | | +-----------+ | 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-parameters" | +-------------------+ 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
__init__ from a variant. It accepts a list of TreeNode
objects; test name
avocado.core.test.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
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
and our values in
/downstream/sleeptest. If we asked for a value using
"*", it’d raise an exception being unable to distinguish whether
we want the value from
/upstream. We can set the
parameter paths to
["/downstream/*", "/upstream/*"] to make all relative
calls (path starting with
*) to first look in nodes in
and if not found look into
Variant is a set of params produced by Varianter`_s and passed to the
test by the test runner as ``params` argument. The simplest variant
None, which still produces an empty AvocadoParams. Also, the
Variant can also be a
tuple(list, paths) or just the
avocado.core.tree.TreeNode with the params.
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:
--json-variants-dumpoption of the
$ 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:
$ avocado run passtest.py --mux-yaml examples/yaml_to_mux/hw/hw.yaml ... $ file $HOME/avocado/job-results/latest/jobdata/variants.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 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) passtest.py:PassTest.test;intel-scsi-56d0: PASS (0.04 s) (2/6) passtest.py:PassTest.test;intel-virtio-3d4e: PASS (0.02 s) (3/6) passtest.py:PassTest.test;amd-scsi-fa43: PASS (0.02 s) (4/6) passtest.py:PassTest.test;amd-virtio-a59a: PASS (0.02 s) (5/6) passtest.py:PassTest.test;arm-scsi-1c14: PASS (0.03 s) (6/6) passtest.py:PassTest.test;arm-virtio-5ce1: PASS (0.04 s) RESULTS : PASS 6 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 | CANCEL 0 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 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
In order to allow force-updating the Varianter it supports
ignore_new_data, which can be used to ignore new data. This is used
by Replay to replace the current run Varianter with the one
loaded from the replayed job. The workflow with
look like this:
avocado run --replay latest -m example.yaml | + replay.run -> Varianter.is_parsed | + replay.run // Varianter object is replaced with the replay job's one | // Varianter.ignore_new_data is set | + job.run_tests -> Varianter.is_parsed | + job._log_variants -> Varianter.to_str | + runner.run_suite -> Varianter.get_number_of_tests | + runner._iter_variants -> Varianter.itertests
The Varianter itself can only produce an empty variant with the `Default params`_, but it invokes all Varianter plugins and if any of them reports variants it yields them instead of the default variant.
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-parameters, 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.
avocado.core.varianter.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
/ path. This is to ensure maximum compatibility with tests
that do not choose an specific parameter location.
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.