Just as relationships go through phases, there are a variety of tests for the partners. Passing these tests indicates if they are worthy of a long term relationship. Each person has their own way to test another, but there are a few common ways people test their partner. Bringing them to meet family and friends is one of the more popular tests. If friends and family don't like a significant other, they tend to speak up immediately.
Some people test their partners in subtle ways. They want to know if the person is open to new experiences. Taking them out for raw sushi or spicy Mexican food might be a test. Asking if their partner would like to try sky diving might be a test to see if they are open to dangerous stunts. Even asking them to go away for a long weekend might be a way to test the partner as well as the relationship.