If its a multiple choice test your professor wont be able to tell through Blackboard if you cheated on the test. Blackboard wouldnt even tell them you cheated if there were short answer questions or fill in the blanks. The only way to find out if people cheated on a multiple choice test is if lots of people get the same easy questions wrong and even then you cant prove it unless the unauthorized test answers are found or someone tells the professor about it. Then the only way they will know about you is if its on your university email or someone pointed you out.
Answers you write can implicate you if several people write the exact same words or even use the exact same methods to answer a question when there are many more ways to do it.
However, professors who give multiple choice exams online probably dont care much that you can cheat or they would not make it so easy.