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 | | |----------------->| | +-------------------+ update defaults +-----------------------+ ^ ^ | | | // default params injected | // All plugins are invoked +--------------------------------------+ | // in turns | +--------------+ +-----------------+ | | | | avocado-virt | | other providers | | | | +--------------+ +-----------------+ | | +--------------------------------------+ | | +----------------------------+-----+ | | | | 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 | + $PLUGIN -> args.default_avocado_params.add_default_param // could be used to insert default values | + 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 Job 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 | + $PLUGIN -> args.default_avocado_params.add_default_param // could be used to insert default values | + replay.run -> Varianter.is_parsed | + replay.run // Varianter object is replaced with the replay job's one | // Varianter.ignore_new_data is set | + $PLUGIN -> args.default_avocado_params.add_default_param // is ignored as new data are not accepted | + 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 Default params is a mechanism to specify default values in Varianter or Varianter plugins. Their purpose is usually to define values dependent on the system which should not affect the test’s results. One example is a qemu binary location which might differ from one host to another host, but in the end they should result in qemu being executable in test. For this reason the Default params do not affects the test’s variant-id (at least not in the official Varianter plugins).
These params can be set from plugin/core by getting
args and using:
default_avocado_params.add_default_parma(self, name, key, value, path=None)
- name - name of the plugin which injects data (not yet used for anything, but we plan to allow white/black listing)
- key - the parameter’s name
- value - the parameter’s value
- path - the location of this parameter. When the path does not exists yet, it’s created out of TreeNode.
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.
Multiplexer or simply
Mux is an abstract concept, which was
the basic idea behind the tree-like params structure with the support
to produce all possible variants. There is a core implementation of
basic building blocks that can be used when creating a custom plugin.
There is a demonstration version of plugin using this concept in
which adds a parser and then
uses this multiplexer concept to define an avocado plugin to produce
- MuxTree - Object which represents a part of the tree and handles the multiplexation, which means producing all possible variants from a tree-like object.
- MuxPlugin - Base class to build Varianter plugins
MuxTreeNode- Inherits from TreeNode and adds the support for control flags (
MuxTreeNode.ctrl) and multiplex domains (
And some support classes and methods eg. for filtering and so on.
A default AvocadoParams tree with variables could look like this:
Multiplex tree representation: ┣━━ paths ┃ → tmp: /var/tmp ┃ → qemu: /usr/libexec/qemu-kvm ┗━━ environ → debug: False
The multiplexer wants to produce similar structure, but also to be able to define not just one variant, but to define all possible combinations and then report the slices as variants. We use the term Multiplex domains to define that children of this node are not just different paths, but they are different values and we only want one at a time. In the representation we use double-line to visibily distinguish between normal relation and multiplexed relation. Let’s modify our example a bit:
Multiplex tree representation: ┣━━ paths ┃ → tmp: /var/tmp ┃ → qemu: /usr/libexec/qemu-kvm ┗━━ environ ╠══ production ║ → debug: False ╚══ debug → debug: True
The difference is that
environ is now a
multiplex node and it’s
children will be yielded one at a time producing two variants:
Variant 1: ┣━━ paths ┃ → tmp: /var/tmp ┃ → qemu: /usr/libexec/qemu-kvm ┗━━ environ ┗━━ production → debug: False Variant 2: ┣━━ paths ┃ → tmp: /var/tmp ┃ → qemu: /usr/libexec/qemu-kvm ┗━━ environ ┗━━ debug → debug: False
Note that the
multiplex is only about direct children, therefore
the number of leaves in variants might differ:
Multiplex tree representation: ┣━━ paths ┃ → tmp: /var/tmp ┃ → qemu: /usr/libexec/qemu-kvm ┗━━ environ ╠══ production ║ → debug: False ╚══ debug ┣━━ system ┃ → debug: False ┗━━ program → debug: True
Produces one variant with
other variant with
As mentioned earlier the power is not in producing one variant, but in defining huge scenarios with all possible variants. By using tree-structure with multiplex domains you can avoid most of the ugly filters you might know from Jenkin’s sparse matrix jobs. For comparison let’s have a look at the same example in avocado:
Multiplex tree representation: ┗━━ os ┣━━ distro ┃ ┗━━ redhat ┃ ╠══ fedora ┃ ║ ┣━━ version ┃ ║ ┃ ╠══ 20 ┃ ║ ┃ ╚══ 21 ┃ ║ ┗━━ flavor ┃ ║ ╠══ workstation ┃ ║ ╚══ cloud ┃ ╚══ rhel ┃ ╠══ 5 ┃ ╚══ 6 ┗━━ arch ╠══ i386 ╚══ x86_64
Variant 1: /os/distro/redhat/fedora/version/20, /os/distro/redhat/fedora/flavor/workstation, /os/arch/i386 Variant 2: /os/distro/redhat/fedora/version/20, /os/distro/redhat/fedora/flavor/workstation, /os/arch/x86_64 Variant 3: /os/distro/redhat/fedora/version/20, /os/distro/redhat/fedora/flavor/cloud, /os/arch/i386 Variant 4: /os/distro/redhat/fedora/version/20, /os/distro/redhat/fedora/flavor/cloud, /os/arch/x86_64 Variant 5: /os/distro/redhat/fedora/version/21, /os/distro/redhat/fedora/flavor/workstation, /os/arch/i386 Variant 6: /os/distro/redhat/fedora/version/21, /os/distro/redhat/fedora/flavor/workstation, /os/arch/x86_64 Variant 7: /os/distro/redhat/fedora/version/21, /os/distro/redhat/fedora/flavor/cloud, /os/arch/i386 Variant 8: /os/distro/redhat/fedora/version/21, /os/distro/redhat/fedora/flavor/cloud, /os/arch/x86_64 Variant 9: /os/distro/redhat/rhel/5, /os/arch/i386 Variant 10: /os/distro/redhat/rhel/5, /os/arch/x86_64 Variant 11: /os/distro/redhat/rhel/6, /os/arch/i386 Variant 12: /os/distro/redhat/rhel/6, /os/arch/x86_64
Versus Jenkin’s sparse matrix:
os_version = fedora20 fedora21 rhel5 rhel6 os_flavor = none workstation cloud arch = i386 x86_64 filter = ((os_version == "rhel5").implies(os_flavor == "none") && (os_version == "rhel6").implies(os_flavor == "none")) && !(os_version == "fedora20" && os_flavor == "none") && !(os_version == "fedora21" && os_flavor == "none")
Which is still relatively simple example, but it grows dramatically with inner-dependencies.
Defines the full interface required by
avocado.core.plugin_interfaces.Varianter. The plugin writer
should inherit from this
MuxPlugin, then from the
and call the:
self.initialize_mux(root, paths, debug)
- root - is the root of your params tree (compound of TreeNode -like nodes)
- paths - is the Parameter paths to be used in test with all variants
- debug - whether to use debug mode (requires the passed tree to be
TreeNodeDebug-like nodes which stores the origin of the variant/value/environment as the value for listing purposes and is __NOT__ intended for test execution.
This is the core feature where the hard work happens. It walks the tree and remembers all leaf nodes or uses list of MuxTrees when another multiplex domain is reached while searching for a leaf.
When it’s asked to report variants, it combines one variant of each remembered item (leaf node always stays the same, but MuxTree circles through it’s values) which recursively produces all possible variants of different multiplex domains.