Add plugins in the test config file.

tests/sample/sigal.conf.py

@@ -8,7 +8,11 @@ keep_orig = True
 links = [('Example link', 'http://example.org'),
          ('Another link', 'http://example.org')]
 
-copyright = "An example copyright message"
+from sigal.plugins import copyright
+plugins = ['sigal.plugins.adjust', copyright]
+copyright = u"© An example copyright message"
+adjust_options = {'color': 0.0, 'brightness': 1.0,
+                  'contrast': 1.0, 'sharpness': 0.0}
 
 # theme = 'galleria'
 # thumb_size = (280, 210)