Added some test-writing docs for plugins, but not sure if they're good. ;)

This commit sponsored by Joe Lee.  Thank you!

docs/source/index.rst

@@ -73,6 +73,7 @@ This guide covers writing new GNU MediaGoblin plugins.
    pluginwriter/quickstart
    pluginwriter/database
    pluginwriter/api
+   pluginwriter/tests
 
 
 Part 4: Developer's Zone

docs/source/pluginwriter/tests.rst

@@ -0,0 +1,64 @@
+.. MediaGoblin Documentation
+
+   Written in 2013 by MediaGoblin contributors
+
+   To the extent possible under law, the author(s) have dedicated all
+   copyright and related and neighboring rights to this software to
+   the public domain worldwide. This software is distributed without
+   any warranty.
+
+   You should have received a copy of the CC0 Public Domain
+   Dedication along with this software. If not, see
+   <http://creativecommons.org/publicdomain/zero/1.0/>.
+
+==============================
+Writing unit tests for plugins
+==============================
+
+Here's a brief guide to writing unit tests for plugins.  However, it
+isn't really ideal.  It also hasn't been well tested... yes, there's
+some irony there :)
+
+Some notes: we're using py.test and webtest for unit testing stuff.
+Keep that in mind.
+
+My suggestion is to mime the behavior of `mediagoblin/tests/` and put
+that in your own plugin, like `myplugin/tests/`.  Copy over
+`conftest.py` and `pytest.ini` to your tests directory, but possibly
+change the `test_app` fixture to match your own tests' config needs.
+For example::
+
+  import pkg_resources
+  # [...]
+
+  @pytest.fixture()
+  def test_app(request):
+      return get_app(
+          request,
+          mgoblin_config=pkg_resources.resource_filename(
+              'myplugin.tests', 'myplugin_mediagoblin.ini'))
+
+In any test module in your tests directory you can then do::
+
+  def test_somethingorother(test_app):
+      # real code goes here
+      pass
+
+And you'll get a mediagoblin application wrapped in webtest passed in
+to your environment.
+
+If your plugin needs to define multiple configuration setups, you can
+actually set up multiple fixtures very easily for this.  You can just
+set up multiple fixtures with different names that point to different
+configs and pass them in as that named argument.
+
+To run the tests, from mediagoblin's directory (make sure that your
+plugin has been added to your mediagoblin checkout's virtualenv!) do::
+
+  ./runtests.sh /path/to/myplugin/tests/
+
+replacing `/path/to/myplugin/` with the actual path to your plugin.
+
+NOTE: again, the above is untested, but it should probably work.  If
+you run into trouble, `contact us
+<http://mediagoblin.org/pages/join.html>`_, preferably on IRC!