It looks like it's something obvious but I can't find the web interface to view simpletest results. Where should I view the errors besides the DB?
If you have drush installed you can run test via command line:
drush test-run YourClassName
The errors will show up after the test is run. Testing from command line is faster than using the UI found at admin/config/development/testing. However you cannot see the succesful steps and the verbose messages.
Between tests make sure yo clean the previous Drupal tables