Add acceptance test to ensure that show_captions has the right effect.

cms/djangoapps/contentstore/features/video.feature

@@ -8,3 +8,8 @@ Feature: Video Component
   Scenario: Creating a video takes a single click
     Given I have clicked the new unit button
     Then creating a video takes a single click
+
+  Scenario: Captions are shown correctly
+    Given I have created a Video component
+    And I have set 'show captions' to false
+    Then when I view the video it does not show the captions by default

cms/djangoapps/contentstore/features/video.py

@@ -16,3 +16,13 @@ def video_takes_a_single_click(step):
     assert(not world.is_css_present('.xmodule_VideoModule'))
     world.css_click("a[data-location='i4x://edx/templates/video/default']")
     assert(world.is_css_present('.xmodule_VideoModule'))
+
+
+@step("I have set 'show captions' to false")
+def set_show_captions_false(step):
+    world.css_click('a.hide-subtitles')
+
+
+@step('when I view the video it does not show the captions by default')
+def does_not_show_captions(step):
+    assert world.css_find('.video')[0].has_class('closed')