Test Classes and the JUnit Test Execution Environment

JUnit sets up the execution environment for tests at the test class file level. I hereby define a Test Class to be any class that contains test methods (test methods were defined in the previous chapter). Test Classes in version JUnit version 4 are a great improvement over version 3.x test classes, which had to subclass a JUnit-provided class. This makes the framework much less invasive and lets you leverage inheritance and other object-oriented features if and where that makes sense.

import java.sql.Connection;
public class HackerTest extends AbstractClientTest {
    private Connection mkConnection() {  // A utility method
        ...

    @org.junit.Test
    void testPasswordGuessing() {
        Connection conn1 = mkConnection();
        ...
        assertEquals(...
    }

    @org.junit.Test(expected=InterruptedException)
    void testTimeout() {
        ...

    @org.junit.After
    protected void deallocateCacheSpace() {
        ....

    @org.junit.After
    protected void deallocateNameTokens() {
        ...

Instance objects which are set up for each test method execution (by @Before methods, and perhaps cleaned up with @After methods) are called Fixtures.

The class contains two test methods, testPasswordGuessing and testTimeout. It also contains two JUnit lifecycle methods, deallocateCacheSpace and deallocateNameTokens. The @Before and @After notations specify methods which will be executed before and after each of your test methods. So, in this case, the method execution sequence would be

JUnit catches all AssertionErrors thrown from test methods, and that is what makes test "failures". If any fixture or test method throws anything else, JUnit will catch it, and that is what makes test "errors". Errors indicate that there is something wrong with your test setup or environment, not with the intended subject of the unit test.

The use of attributes is a great improvement over JUnit verision 3.x, where the single allowed setup and single allowed cleanup methods were pre-defined.

There are also @BeforeClass and @AfterClass lifecycle attributes. @BeforeClass doesn't do anything that you couldn't do just as well in the class constructor. but @AfterClass methods can be useful for performing final cleanup after all test methods (and @Afters) in a single test class have completed.