Whenever a new bug is found, the tester will need to create a defect in the defect tracking system they work with. This defect needs to contain clear steps to reproduce the problem, so that developers can identify the root cause of the issue. Here are some tips regarding bugs and reproducing them.
When writing tests that require the generation of random strings, a very useful class can come in handy, namely RandomStringUtils from the Apache Commons Langs utilities library. It can be used for generating string that contain only letters, only numbers, both, these and other characters.