There are 4 important features;

-Fixtures is a fixed state of a set of objects used as a baseline 
for running tests. The purpose of a test fixture is to ensure that 
there is a well known and fixed environment in which tests are run so 
that results are repeatable. It includes setup and teardown methods
setUp() method which runs before every test invocation.
tearDown() method which runs after every test method.

-Test suites
-Test runners
-JUnit classes