You can access tests from multiple areas including from the Activity Stream or in the Calendar (both are in the main Blackboard menu) if your instructor added due dates. Here is an example of a test appearing in a student's Activity Stream:

You can also find tests inside of your Course Content page, here is an example of a test on a Course Content learning module:

After you select a test, the Details & Information panel appears which includes the due date, number of attempts allowed, if there is a time limit for taking the test, and possibly rubric for grading.