[Avocado-devel] [RFC] Pre/Post test hooks

[Lukáš Doktor]

Dne 1.4.2016 v 16:00 Cleber Rosa napsal(a):
> MOTIVATION
> ==========
>
> The idea of adding hooks to be run by Avocado before and after tests is
> general enough, and may be used by the community in unpredictable ways.
> And that is good.
>
> For this team, the initial motivation was to be able to bring back an
> Autotest feature that some of our users are missing: the ability to set
> the system-wide "kernel core pattern" configuration for tests.
>
> Having a pre-test hook would allow "/proc/sys/kernel/core_pattern" to be
> read, saved and modified to point to the test results directory. Having
> a post-test hook would allow "/proc/sys/kernel/core_pattern" to be
> reverted back to its original state.
>
> Other currently core features such as sysinfo collection, could be
> re-implemented as pre/post test hooks.
>
> GENERAL DESIGN POINTS
> =====================
>
> These are the most important design decisions to be acknowledged or
> questioned. Please reply with either ACK or your questions/suggestions.
>
> 1) Hooks are implemented as plugin classes, based on a given defined
> interface, in the same way current "CLICmd" and "CLI" interfaces allow
> plugin writers to extend Avocado and give it new commands and command
> line options.
I'd prefer "pluginizing" the whole "runner" instead of custom pre and 
post classes. What am I talking about:

The CLICmd and CLI allows one to add several methods + "run" method 
which is executed to do the action. It makes sense for CLI, but IMO it 
does not suit this case.

Instead we can create plugin interface which allows to do things on 
certain occasions (hooks), one of them `start_test` and `stop_test`. 
It's similar to `ResultsProxy`, `LoaderProxy`, ....

They both can achieve the same, the main reason is convenience:

The CLI-like:

+ clearly defines the interface
+ adds itself by publishing itself into the correct namespace
- for pre+post plugins requires double plugin initialization
- to reuse information from pre-hook in post-hook one needs to store the 
state inside the results.

The *Proxy-like:

+ defines the interface
+ adds itself by publishing itself into the correct namespace
+ pre+post plugins are initialized just once (pure pre-plugins define 
only `pre_test` hook, post-plugins only `post_test` hook...)
+ the state is preserved throughout the execution, so one can store the 
details inside `self`.
+ is easily extensible of another hooks related to this

Details in 
https://github.com/avocado-framework/avocado/pull/1106#discussion_r58193746


>
> 2) The hooks are executed by the *runner*, and not by the test process.
> The goal is not interfere with the test itself. The pre and post code
> that runs before and after the test should not *directly* change the
> test behavior and outcome. Of course, the test environment can be
> changed in a way (say having packages removed) that a test may fail
> because of hook actions.
ACK

>
> 3) Test execution time should not be changed by pre and post hooks. If a
> pre-test hook takes "n" seconds to run, "n" should not be added to the
> test run time.
ACK

>
> 4) Job run time: right now, Avocado times a Job based on the sum of
> individual test run times. With pre and post test hooks, this can be
> very different from job "wall clock" times. My instinct is to change
> that, so that a Job run time is the job "wall clock" time. I'm unsure if
> we should add yet another time measure, that is, the sum of individual
> test run time. This is also bound to be broken when parallel run of
> tests is implemented.
I'm fine with either "real time" `time.time - start`, or with the 
"user+sys time" `sum(test.time for test in job.tests)` (so sum of all 
test times). I don't think we should do anything smart in here as it 
might be misleading.

     time stress -c 8 -t 10
     stress: info: [23182] dispatching hogs: 8 cpu, 0 io, 0 vm, 0 hdd
     stress: info: [23182] successful run completed in 10s

     real    0m10.001s
     user    1m19.005s
     sys     0m0.003s


>
> 5) The pre test hook is given the test "early status". Information such
> as the test tagged name, the fact that it has not yet started to run and
> the test results directory are all part of the early status.
Does it means the test execution would wait for the pre-job hooks 
completion? It's logical, but currently it requires bi-directional 
communication with the runner (not after the Test/runner cleanup).

Anyway yes, the pre-job should get the early status with all benefits 
and drawbacks. Users are responsible to understand them.

>
> 6) Because of point #5, the test is instantiated on the test process,
> its early state is sent, but the test execution itself is held until the
> runner finishes running the pre-test hooks.
OMG, I should first read and then think... For now, yes, but once we 
move the test workflow from test to runner (as proposed in the 
https://trello.com/c/W58vhyHR/539-bug-some-avocado-test-methods-and-atributes-are-public 
).

PS: The pre and post test hooks are acctually also mentioned in that card...

>
> 7) The post test hook is given the last test status, which is also used
> by the runner to identify test success, failure, etc.
Yep

>
>
> Thanks,
>   - Cleber.
>