Here are some problems I faced when adding selenium to a Drupal7 project I have been working on
1-Test cases are not listed.
Description: when installing the latest Selenium & SimpleTest modules, anything except selenium default tests are not listed in the Configuration/Testing
Fast Solution: Use latest Selenium module with the default SimpleTest module installed with Drupal core.
2-Running the test case randomly opens new default Drupal installation.
Description: Simple test is configured to clone the database structure and perform the test cases on this new database so you will not find any of your themes/modules enabled, In some cases the test user created will not be able to login.
Typical Solution: enable the themes/modules when setting up the test and run the patch file shipped with Selenium module without editing it.
Another Solution: run the test cases on the same database (a backup of it of course or whatever!), and this can be done with the following steps
a-Extending the DrupalSeleniumWebTestCase class
class DrupalSeleniumCustomTestCase extends DrupalSeleniumWebTestCase {
public $onOriginal = TRUE;