Docs for behave tests

This commit adds an explaining comment to @flindenberg's PR #174. I also
forgot to add a few lines to the README about how to run the behave
tests. And I removed Chris' overly optimistic statement that we're using
TDD.

README.md

@@ -166,13 +166,10 @@ If you just use "python manage.py create_dummy_data 5" without --flush it is NOT
 
 ### Running Tests
 
-*Note*: we're committed to testing and hope, the next paragraph will not be a lie any longer soon :-) 
+Feature PR should be accompanied by appropriate test. We have unit and integration tests that
+are run with `py.test`, and functional/behave tests that are run with `selenium`.
 
-We are using test driven development (TDD) with [py.test](http://pytest.org/). 
-
-A good read on TDD is the free o'Reilly eBook ["Test-Driven Development with Python"](http://chimera.labs.oreilly.com/books/1234000000754/index.html)
-
-To run the tests, run the following command (with your virtual env activated, see 3.)
+To run unit tests, run the following command (with your virtual env activated, see 3.)
 
     $ py.test -v [/path/to/volunteer_planner.git/]
 
@@ -184,6 +181,10 @@ This generates a nice HTML coverage page, to poke around which can be found at `
 
 *Note*: The directory `htmlcov` is git-ignored.
 
+To run selenium tests, run
+
+    $ behave tests/_behave
+
 ### Translations
 
 We use [Transifex (tx)](https://www.transifex.com/coders4help/volunteer-planner/) for managing translations.

tests/_behave/environment.py

@@ -9,6 +9,9 @@ def before_all(context):
     Steps to be executed before behave features are run.
     Serves to fire up PhantomJS.
     """
+    # Our tests all test against the source strings (English), so we force PhantomJS to
+    # request pages in that language instead of the system's locale.
+    # http://stackoverflow.com/a/17862456
     webdriver.DesiredCapabilities.PHANTOMJS['phantomjs.page.customHeaders.Accept-Language'] = 'en-US'
     context.browser = webdriver.PhantomJS()