clear existing assets before copying new assets

pavelib/assets.py

@@ -632,7 +632,7 @@ def collect_assets(systems, settings):
     `settings` is the Django settings module to use.
     """
     for sys in systems:
-        sh(django_cmd(sys, settings, "collectstatic --noinput > /dev/null"))
+        sh(django_cmd(sys, settings, "collectstatic --clear --noinput"))
         print("\t\tFinished collecting {} assets.".format(sys))
 
 

pavelib/paver_tests/test_servers.py

@@ -27,7 +27,7 @@ EXPECTED_PREPROCESS_ASSETS_COMMAND = (
     u" {system}/static/sass/*.scss {system}/static/themed_sass"
 )
 EXPECTED_COLLECT_STATIC_COMMAND = (
-    u"python manage.py {system} --settings={asset_settings} collectstatic --noinput > /dev/null"
+    u"python manage.py {system} --settings={asset_settings} collectstatic --clear --noinput"
 )
 EXPECTED_CELERY_COMMAND = (
     u"python manage.py lms --settings={settings} celery worker --beat --loglevel=INFO --pythonpath=."