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Write a document on how to add a test to Stem

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Sebastian Hahn 2016-03-28 17:20:48 +02:00
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doc/HACKING/WritingTests.md
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@ -417,18 +417,50 @@ makefile exports them.
Writing integration tests with Stem
-----------------------------------
The 'stem' library includes extensive unit tests for the Tor controller
protocol.
For more information on writing new tests for stem, have a look around
the `test/*` directory in stem, and find a good example to emulate. You
might want to start with
`https://gitweb.torproject.org/stem.git/tree/test/integ/control/controller.py`
to improve Tor's test coverage.
The 'stem' library includes extensive tests for the Tor controller protocol.
You can run stem tests from tor with `make test-stem`, or see
`https://stem.torproject.org/faq.html#how-do-i-run-the-tests`.
To see what tests are available, have a look around the `test/*` directory in
stem. The first thing you'll notice is that there are both `unit` and `integ`
tests. The former are for tests of the facilities provided by stem itself that
can be tested on their own, without the need to hook up a tor process. These
are less relevant, unless you want to develop a new stem feature. The latter,
however, are a very useful tool to write tests for controller features. They
provide a default environment with a connected tor instance that can be
modified and queried. Adding more integration tests is a great way to increase
the test coverage inside Tor, especially for controller features.
Let's assume you actually want to write a test for a previously untested
controller feature. I'm picking the `exit-policy/*` GETINFO queries. Since
these are a controller feature that we want to write an integration test for,
the right file to modify is
`https://gitweb.torproject.org/stem.git/tree/test/integ/control/controller.py`.
First off we notice that there is an integration test called
`test_get_exit_policy()` that's already written. This exercises the interaction
of stem's `Controller.get_exit_policy()` method, and is not relevant for our
test since there are no stem methods to make use of all `exit-policy/*`
queries (if there were, likely they'd be tested already. Maybe you want to
write a stem feature, but I chose to just add tests).
Our test requires a tor controller connection, so we'll use the
`@require_controller` annotation for our `test_exit_policy()` method. We need a
controller instance, which we get from
`test.runner.get_runner().get_tor_controller()`. The attached Tor instance is
configured as a client, but the exit-policy GETINFO queries need a relay to
work, so we have to change the config (using `controller.set_options()`). This
is OK for us to do, we just have to remember to set DisableNetwork so we don't
actually start an exit relay and also to undo the changes we made (by calling
`controller.reset_conf()` at the end of our test). Additionally, we have to
configure a static Address for Tor to use, because it refuses to build a
descriptor when it can't guess a suitable IP address. Unfortunately, these
kinds of tripwires are everywhere. Don't forget to file appropriate tickets if
you notice any strange behaviour that seems totally unreasonable.
Check out the `test_exit_policy()` function in abovementioned file to see the
final implementation for this test.
System testing with Chutney
---------------------------