[Avocado-devel] [RFC] Environment Variables

[Amador Pahim]

Hi folks,

We have requests to handle the environment variables that we can set to 
the tests. This is the RFC in that regard, with a summary of the ideas 
already exposed in the original request and some additional planning.

The original request is here: 
https://trello.com/c/Ddcly0oG/312-mechanism-to-provide-environment-variables-to-tests-run-on-a-virtual-machine-remote

Motivation
==========
Avocado tests are executed in a fork process or even in a remote 
machine. Regardless the fact that Avocado is hard coded to set some 
environment variables, they are for internal consumption and user is not 
allowed to control/configure its behavior.
The motivation is the request to provide users an interface to set 
and/or keep environment variables for test consumption.

Use cases
=========
1) Use the command line or the config file to set the environment 
variables in tests processes environment; access those variables from 
inside the test.
2) Copy from current environment some environment variable(s) to the 
tests processes environment; access those variables from inside the test.

Proposal
========
- To create a command line option, under the `run` command, to set 
environment variables that will be available in tests environment process:

  $ avocado run --test-env='FOO=BAR,FOO1=BAR1' passtest.py

- To create an option in config file with a dictionary of environment 
variables to set in test process environment. It can be used as a 
replacement or complement to the command line option (with lower priority):

  [tests.env]
  test_env_vars = {'FOO': 'BAR', 'FOO1': 'BAR1'}

- Create an option in config file with a list of environment variable 
names to copy from avocado main process environment to the test process 
environment (similar to env_keep in the /etc/sudoers file):

  [tests.env]
  env_keep = ['FOO', 'FOO1', 'FOO2']


For every configuration entry point, the setting have to be respected in 
local and remote executions.

Drawbacks
=========

While setting an environment variable, user will be able to change the 
behavior of a test and probably the behavior of Avocado itself. Maybe 
even the OS behavior as well. We should:
- Warn users about the danger when using such options.
- Protect Avocado environment variables from overwriting.


Looking forward to read your comments.

Best Regards,
--
Amador Pahim