There are a number of test users and organisations used during development.
The users are: mmm, test1, test2, test3 and test4. The passwords are the same as the usernames. The user mmm is the best user with which to test - the others are handy when trying testing a lesson with multiple users.
There are also a series of test organisations. The safest ones to play with are Playpen (course) and its single class Everybody. For extensive testing, the MATH111 course offers two classes and the test1, test2, test3 and test4 users are split across the two classes. But you will need to look in the database to see who is in which organisation and with which roles.