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



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.

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.

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.

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.

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.

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.

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


Thanks,
 - Cleber.

--
Cleber Rosa
[ Sr Software Engineer - Virtualization Team - Red Hat ]
[ Avocado Test Framework - avocado-framework.github.io ]


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