Default to local database when DATABASE_URL not set.

Author: dblock

spec/database_adapters/mongoid/mongoid.yml

@@ -11,7 +11,7 @@ development:
 test:
   clients:
     default:
-      uri: <%= ENV["DATABASE_URL"] %>
+      uri: <%= ENV["DATABASE_URL"] || 'mongodb://localhost' %>
   options:
     raise_not_found_error: false
     use_utc: true