[Avocado-devel] RFC: Nested tests (previously multi-stream test) [v5]
Cleber Rosa
crosa at redhat.com
Wed May 25 19:18:38 UTC 2016
On 05/24/2016 11:53 AM, Lukáš Doktor wrote:
> Hello guys,
>
> this version returns to roots and tries to define clearly the single
> solution I find teasing for multi-host and other complex tests.
>
> Changes:
>
> v2: Rewritten from scratch
> v2: Added examples for the demonstration to avoid confusion
> v2: Removed the mht format (which was there to demonstrate manual
> execution)
> v2: Added 2 solutions for multi-tests
> v2: Described ways to support synchronization
> v3: Renamed to multi-stream as it befits the purpose
> v3: Improved introduction
> v3: Workers are renamed to streams
> v3: Added example which uses library, instead of new test
> v3: Multi-test renamed to nested tests
> v3: Added section regarding Job API RFC
> v3: Better description of the Synchronization section
> v3: Improved conclusion
> v3: Removed the "Internal API" section (it was a transition between
> no support and "nested test API", not a "real" solution)
> v3: Using per-test granularity in nested tests (requires plugins
> refactor from Job API, but allows greater flexibility)
> v4: Removed "Standard python libraries" section (rejected)
> v4: Removed "API backed by cmdline" (rejected)
> v4: Simplified "Synchronization" section (only describes the
> purpose)
> v4: Refined all sections
> v4: Improved the complex example and added comments
> v4: Formulated the problem of multiple tasks in one stream
> v4: Rejected the idea of bounding it inside MultiTest class
> inherited from avocado.Test, using a library-only approach
> v5: Avoid mapping ideas to multi-stream definition and clearly
> define the idea I bear in my head for test building blocks
> called nested tests.
>
>
> Motivation
> ==========
>
> Allow building complex tests out of existing tests producing a single
> result depending on the complex test's requirements. Important thing is,
> that the complex test might run those tests on the same, but also on a
> different machine allowing simple development of multi-host tests. Note
> that the existing tests should stay (mostly) unchanged and executable as
> simple scenarios, or invoked by those complex tests.
>
> Examples of what could be implemented using this feature:
>
> 1. Adding background (stress) tasks to existing test producing
> real-world scenarios.
> * cpu stress test + cpu hotplug test
> * memory stress test + migration
> * network+cpu+memory test on host, memory test on guest while
> running migration
> * running several migration tests (of the same and different type)
>
> 2. Multi-host tests implemented by splitting them into components and
> leveraging them from the main test.
> * multi-host migration
> * stressing a service from different machines
>
>
> Nested tests
> ============
>
> Test
> ----
>
> A test is a receipt explaining prerequisites, steps to check how the
> unit under testing behaves and cleanup after successful or unsuccessful
> execution.
>
You probably meant "recipe" instead of "receipt". OK, so this is an
abstract definition...
> Test itself contains lots of neat features to simplify logging, results
> analysis and error handling evolved to simplify testing.
>
... while this describes concrete conveniences and utilities that users
of the Avocado Test class can expect.
> Test runner
> -----------
>
> Is responsible for driving the test(s) execution, which includes the
> standard test workflow (setUp/test/tearDown), handle plugin hooks
> (results/pre/post) as well as safe interruption.
>
OK.
> Nested test
> -----------
>
> Is a test invoked by other test. It can either be executed in foreground
I got from this proposal that a nested test always has a parent. Basic
question is: does this parent have to be a regular (that is, non-nested)
test?
Then, depending on the answer, the following question would also apply:
do you believe a nesting level limit should be enforced?
> (while the main test is waiting) or in background along with the main
> (and other background tests) test. It should follow the default test
> workflow (setUp/test/tearDown), it should keep all the neat test feature
> like logging and error handling and the results should also go into the
> main test's output, with the nested test's id as prefix. All the
> produced files of the nested test should be located in a new directory
> inside the main test results dir in order to be able to browse either
> overall results (main test + nested tests) or just the nested tests ones.
>
Based on the example given later, you're attributing to the NestedRunner
the responsibility to put the nested test results "in the right"
location. It sounds appropriate. The tricky questions are really how
they show up in the overall job/test result structure, because that
reflects how much the NestedRunner looks like a "Job".
> Resolver
> --------
>
> Resolver is an avocado component resolving a test reference into a list
> of test templates compound of the test name, params and other
> `avocado.Test.__init__` arguments.
>
> Very simple example
> -------------------
>
> This example demonstrates how to use existing test (SimpleTest
> "/usr/bin/wget example.org") in order to create a complex scenario
> (download the main page from example.org from multiple computers almost
> concurrently), without any modifications of the `SimpleTest`.
>
> import avocado
>
> class WgetExample(avocado.Test):
> def test(self):
> # Initialize nested test runner
> self.runner = avocado.NestedRunner(self)
> # This is what one calls on "avocado run"
> test_reference = "/usr/bin/wget example.org"
> # This is the resolved list of templates
> tests = avocado.resolver.resolve(test_reference)
> # We could support list of results, but for simplicity
> # allow only single test.
> assert len(tests) == 1, ("Resolver produced multiple test "
> "names: %s\n%s" % (test_reference,
> tests)
> test = tests[0]
> for machine in self.params.get("machines"):
> # Query a background job on the machine (local or
> # remote) and return test id in order to query for
> # the particular results or task interruption, ...
> self.runner.run_bg(machine, test)
> # Wait for all background tasks to finish, raise exception
> # if any of them fails.
> self.runner.wait(ignore_errors=False)
>
Just for accounting purposes at this point, and not for applying
judgment, let's take note that this approach requires the following sets
of APIs to become "Test APIs":
* avocado.NestedRunner
* avocado.resolver
Now, doing a bit of judgment. If I were an Avocado newcomer, looking at
the Test API docs, I'd be intrigued at how these belong to the same very
select group that includes only:
* avocado.Test
* avocado.fail_on
* avocado.main
* avocado.VERSION
I'm not proposing a different approach or a different architecture. If
the proposed architecture included something like a NestedTest class,
then probably the feeling is that it would indeed naturally belong to
the same group. I hope I managed to express my feeling, which may just
be overreaction. If others share the same feeling, then it may be a sign
of a red flag.
Now, considering my feeling is not an overreaction, this is how such an
example could be written so that it does not put NestedRunner and
resolver in the Test API namespace:
from avocado import Test
from avocado.utils import nested
class WgetExample(Test):
def test(self):
reference = "/usr/bin/wget example.org"
tests = []
for machine in self.params.get("machines"):
tests.append(nested.run_test_reference(self, reference,
machine))
nested.wait(tests, ignore_errors=False)
This would solve the crossing (or pollution) of the Test API namespace,
but it has a catch: the test reference resolution is either included in
`run_test_reference` (which is a similar problem) or delegated to the
remote machine. Having the reference delegated sounds nice, until you
need to identify backing files for the tests and copy them over to the
remote machine. So, take this as food for thought, and not as a fail
proof solution.
> When nothing fails, this usage has no benefit over the simple logging
> into a machine and firing up the command. The difference is, when
> something does not work as expected. With nested test, one get a runner
> exception if the machine is unreachable. And on test error he gets not
> only overall log, but also the per-nested-test results simplifying the
> error analysis. For 1, 2 or 3 machines, this makes no difference, but
> imagine you want to run this from hundreds of machines. Try finding the
> exception there.
>
I agree that it's nice to have the nested tests' logs. What you're
proposing is *core* (as in Test API) convenience, over something like:
from avocado import Test
from avocado.utils import nested
class WgetExample(Test):
def test(self):
reference = "/usr/bin/wget example.org"
tests = []
for machine in self.params.get("machines"):
tests.append(nested.run_test_reference(self, reference,
machine))
nested.wait(tests, ignore_errors=False)
nested.save_results(tests,
os.path.join(self.resultsdir, "nested"))
> Yes, you can implement the above without nested tests, but it requires a
> lot of boilerplate code to establish the connection (or raise an
> exception explaining why it was not possible and I'm not talking about
> "unable to establish connection", but granularity like "Invalid
> password", "Host is down", ...). Then you'd have to setup the output
> logging for that particular task, add the prefix, run the task (handling
> all possible exceptions) and interpret the results. All of this to get
> the same benefits very simple avocado test provides you.
>
Having boiler plate code repeatedly written by users is indeed not a
good thing. And a well thought out API for users is the way to prevent
boiler plate code from spreading around in tests.
The exception handling, that is, raising exceptions to flag failures in
the nested tests execution is also a given IMHO.
> Advanced example
> ----------------
>
> Imagine a very complex scenario, for example a cloud with several
> services. One could write a big-fat test tailored just for this scenario
> and keep adding sub-scenarios producing unreadable source code.
>
> With nested tests one could split this task into tests:
>
> * Setup a fake network
> * Setup cloud service
> * Setup in-cloud service A/B/C/D/...
> * Test in-cloud service A/B/C/D/...
> * Stress network
> * Migrate nodes
>
> New variants could be easily added, for example DDoS attack to some
> nodes, node hotplug/unplug, ... by invoking those existing tests and
> combining them into a complex test.
>
> Additionally note that some of the tests, eg. the setup cloud service
> and setup in-cloud service are quite generic tests, what could be reused
> many times in different tests. Yes, one could write a library to do
> that, but in that library he'd have to handle all exceptions and provide
> nice logging, while not clutter the main output with unnecessary
> information.
>
> Job results
> -----------
>
> Combine (multiple) test results into understandable format. There are
> several formats, the most generic one is file format:
>
> .
> ├── id -- id of this job
> ├── job.log -- overall job log
> └── test-results -- per-test-directories with test results
> ├── 1-passtest.py:PassTest.test -- first test's results
> └── 2-failtest.py:FailTest.test -- second test's results
>
> Additionally it contains other files and directories produced by avocado
> plugins like json, xunit, html results, sysinfo gathering and info
> regarding the replay feature.
>
OK, this is pretty much a review.
> Test results
> ------------
>
> In the end, every test produces results, which is what we're interested
> in. The results must clearly define the test status, should provide a
> record of what was executed and in case of failure, they should provide
> all the information in order to find the cause and understand the failure.
>
> Standard tests does that by providing test log (debug, info, warning,
> error, critical), stdout, stderr, allowing to write to whiteboard and
> attach files in the results directory. Additionally due to structure of
> the test one knows what stage(s) of the test failed and pinpoint exact
> location of the failure (traceback in the log).
>
> .
> ├── data -- place for other files produced by a test
> ├── debug.log -- debug, info, warn, error log
> ├── remote.log -- additional log regarding remote session
> ├── stderr -- standard error
> ├── stdout -- standard output
> ├── sysinfo -- provided by sysinfo plugin
> │ ├── post
> │ ├── pre
> │ └── profile
> └── whiteboard -- file for arbitrary test data
>
> I'd like to extend this structure of either a directory "subtests", or
> convention for directories intended for nested test results `r"\d+-.*"`.
>
Having them on separate sub directory is less intrusive IMHO. I'd even
argue that `data/nested` is the way to go.
> The `r"\d+-.*"` reflects the current test-id notation, which nested
> tests should also respect, replacing the serialized-id by
> in-test-serialized-id. That way we easily identify which of the nested
> tests was executed first (which does not necessarily mean it finished as
> first).
>
> In the end nested tests should be assigned a directory inside the main
> test's results (or main test's results/subtests) and it should produce
> the data/debug.log/stdout/stderr/whiteboard in there as well as
> propagate the debug.log with a prefix to the main test's debug.log (as
> well as job.log).
>
> └── 1-parallel_wget.py:WgetExample.test -- main test
> ├── data
> ├── debug.log -- contains main log + nested logs with prefixes
> ├── remote.log
> ├── stderr
> ├── stdout
> ├── sysinfo
> │ ├── post
> │ ├── pre
> │ └── profile
> ├── whiteboard
> ├── 1-_usr_bin_wget\ example.org -- first nested test
> │ ├── data
> │ ├── debug.log -- contains only this nested test log
> │ ├── remote.log
> │ ├── stderr
> │ ├── stdout
> │ └── whiteboard
> ├── 2-_usr_bin_wget\ example.org -- second nested test
> ...
> └── 3-_usr_bin_wget\ example.org -- third nested test
> ...
>
> Note that nested tests can finish with any result and it's up to the
> main test to evaluate that. This means that theoretically you could find
> nested tests which states `FAIL` or `ERROR` in the end. That might be
> confusing, so I think the `NestedRunner` should append last line to the
> test's log saying `Expected FAILURE` to avoid confusion while looking at
> results.
>
This special injection, and special handling for that matter, actually
makes me more confused.
> Note2: It might be impossible to pass messages in real-time across
> multiple machines, so I think at the end the main job.log should be
> copied to `raw_job.log` and the `job.log` should be reordered according
> to date-time of the messages. (alternatively we could only add a contrib
> script to do that).
>
Definitely no to another special handling. Definitely yes to a post-job
contrib script that can reorder the log lines.
>
> Conclusion
> ==========
>
> I believe nested tests would help people covering very complex scenarios
> by splitting them into pieces similarly to Lego. It allows easier
> per-component development, consistent results which are easy to analyze
> as one can see both, the overall picture and the specific pieces and it
> allows fixing bugs in all tests by fixing the single piece (nested test).
>
It's pretty clear that running other tests from tests is *useful*,
that's why it's such a hot topic and we've been devoting so much energy
to discussing possible solutions. NestedTests is one to do it, but I'm
not confident we have enough confidence to make it *the* way to do it.
The feeling that I have at this point, is that maybe we should prototype
it as utilities to:
* give Avocado a kickstart on this niche/feature set
* avoid as much as possible user-written boiler plate code
* avoid introducing *core* test APIs that would be set in stone
The gotchas that we have identified so far, are IMHO, enough to restrain
us from forcing this kind of feature into the core test API, which we're
in fact, trying to clean up.
With user exposition and feedback, this, a modified version or a
completely different solution, can evolve into *the* core (and
supported) way to do it.
--
Cleber Rosa
[ Sr Software Engineer - Virtualization Team - Red Hat ]
[ Avocado Test Framework - avocado-framework.github.io ]
More information about the Avocado-devel
mailing list