Tests include 1 to Several tests cases
It may be that some test cases are common to multiple tests.
You can create a library of reusable tests cases from the Assets module on the sidebar.
From here, you'll be able to create reusable testcases.
Then, when you are on a test, you'll be able to reference a reusable test case and incorporate it in the test.
Reference in user's manual: Assets reusable testcase