One of the most significant innovations introduced in JUnit 4 was the use of rules. Rules allow flexible addition or redefinition of the behavior of each test method in a test class. A rule should be included in a test case by annotating a class attribute with the annotation @Rule. The type of this attribute should inherit the JUnit interface org.junit.rulesTestRule. The following rules are provided out of the box in JUnit 4:

• ErrorCollector: This rule allows execution of a test to continue after the first problem is found
• ExpectedException: This rule allows to verify that a test throws a specific exception
• ExternalResource: This rule provides a base class for Rules that set up an external resource before a test (a file, socket, server, database connection, and so on) and guarantee to tear it down afterward
• TestName: This rule makes the current test name available inside test methods
• TemporaryFolder: This rule allows creation of files and folders that should be deleted when the test method finishes
• Timeout: This rule applies the same timeout to all test methods in a class
• TestWatcher: It is a base class for rules that will keep a log of each passing and failing test

Another advance JUnit 4 features allow to:

• Execute tests is a given order, using the annotation @FixMethodOrder.
• Create assumptions using the class Assume. This class offers many static methods, such as assumeTrue(condition), assumeFalse(condition), assumeNotNull(condition), and assumeThat(condition). Before executing a test, JUnit checks the assumptions present in the test. If one of the assumptions fail, the JUnit runner ignores the tests with failing assumptions.
• JUnit provides a timeout value (in milliseconds) in the @Test annotation to make sure that if a test runs longer than the specified value, the test fails.
• Categorize tests using the test runner Categories and identify the types of test annotating the tests method with the annotation Category.