Test interfaces

In JUnit 5, there are different rules relative to the use of annotations in Java interfaces. First of all, we need to be aware that @Test, @TestFactory, @BeforeEach, and @AfterEach can be declared on interface default methods.

Note

Default methods is a feature of Java introduced in version 8. These methods (declared using the reserve keyword default) allows to define a default implementation for a given method within a Java interface. This capability can be useful for backward compatibility with existing interfaces.

The second rule regarding JUnit 5 and interfaces is that @BeforeAll and @AfterAll can be declared on static methods in a test interface. Moreover, if the test class, which implements a given interface, is annotated with @TestInstance(Lifecycle.PER_CLASS), the methods @BeforeAll and @AfterAll declared on the interface do not need to be static, but defaultmethods.

The third and final rule concerning interfaces in JUnit 5 is @ExtendWith and @Tag can be declared on test...