JUnit testing takes place in a traditional Java class, just like the classes written for the application you want to test. The functionality for those tests comes from JUnit classes, most commonly the Assert class and annotation classes.

“Annotating” is a general term that refers to ways of marking methods for testing, changing how these methods are compiled, and establishing when they’ll be run by the compiler. The four most essential annotations are @Before, @Test, @After, and @Ignore.

The above annotations can be imported in the following ways:

import org.junit.Before;
import org.junit.Test;
import org.junit.After;
import org.junit.Ignore;

Additionally, the following line will grab all functionality from the Assert class library, but note that each assert method can be imported individually:

import static org.junit.Assert.*;

Let’s cover what all these annotations and classes mean and how they’re used for JUnit testing!