Test parameters¶
Note
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.varianter.AvocadoParams
type.
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 variant to produce AvocadoParams
| Test |
| |
+-----^-----+
| // single variant is passed to Test
|
+-----------+
| Runner | // iterates through tests and variants to run all
+-----^-----+ // desired combinations specified by "--execution-order"
|
|
+-------------------+ 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.
Test’s default params¶
avocado.core.test.Test.default_params
Every (instrumented) test can hardcode default params by storing a dict
in self.default_params
. This attribute is checked during
avocado.core.test.Test
‘s __init__
phase and if present it’s
used by AvocadoParams.
Warning
Don’t confuse Test’s default params with Default params
TreeNode¶
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.
AvocadoParams¶
avocado.core.varianter.AvocadoParams
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.TestName
(for logging purposes); list of
default paths (Mux path) and the Test’s default params.
In test it allows querying for data by using:
self.params.get($name, $path=None, $default=None)
Where:
- 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.
Mux path¶
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
mux path 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 mux path is in Yaml_to_mux plugin in Resolution order section.
Variant¶
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
is None
, which still produces AvocadoParams with only the
Test’s default params. If dict is used as a Variant, it (safely)
updates the default params. Last but not least the Variant can also
be a tuple(list, mux_path)
or just the list
of
avocado.core.tree.TreeNode
with the params.
Varianter¶
avocado.core.varianter.Varianter
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 ignore_new_data
could
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 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.
Default params¶
Unlike Test’s default params 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 default_avocado_params
from args
and using:
default_avocado_params.add_default_parma(self, name, key, value, path=None)
Where:
- 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.
Varianter plugins¶
avocado.core.plugin_interfaces.Varianter
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¶
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
avocado_varianter_yaml_to_mux
which adds a parser and then
uses this multiplexer concept to define an avocado plugin to produce
variants from yaml
(or json
) files.
Multiplexer concept¶
As mentioned earlier, this is an in-core implementation of building blocks intended for writing Varianter plugins based on a tree with Multiplex domains defined. The available blocks are:
- 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 (MuxTreeNode.multiplex
).
And some support classes and methods eg. for filtering and so on.
Multiplex domains¶
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 /paths
and /environ/production
and
other variant with /paths
, /environ/debug/system
and
/environ/debug/program
.
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
Which produces:
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.
MuxPlugin¶
Defines the full interface required by
avocado.core.plugin_interfaces.Varianter
. The plugin writer
should inherit from this MuxPlugin
, then from the Varianter
and call the:
self.initialize_mux(root, mux_path, debug)
Where:
- root - is the root of your params tree (compound of TreeNode -like nodes)
- mux_path - is the Mux path to be used in test with all variants
- debug - whether to use debug mode (requires the passed tree to be
compound of
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 method must be called before the Varianter‘s second stage
(the latest opportunity is during self.update_defaults
). The
MuxPlugin‘s code will take care of the rest.
MuxTree¶
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.