How To Write Setup Code to Run Once for All Test

Interview Questions

How To Write Setup Code to Run Once for All Tests in a Test Class?

JUnit Questions and Answers

How To Write Setup Code to Run Once for All Tests in a Test Class?

From the previous question, you know that if you write a setup code under the "@Before" annotation, it will be executed many times: once per each test in the test class.

Is there any way to write a setup code that will be executed only once for all tests in a single test class? The answer is YES. Here is how the JUnit FAQ answers this question in details:

The desire to do this is usually a symptom of excessive coupling in your design. If two or more tests must share the same test fixture state, then the tests may be trying to tell you that the classes under test have some undesirable dependencies.

Refactoring the design to further decouple the classes under test and eliminate code duplication is usually a better investment than setting up a shared test fixture.

But if you must...

You can add a @BeforeClass annotation to a method to be run before all the tests in a class, and a @AfterClass annotation to a method to be run after all the tests in a class. Here's an example:

    package junitfaq;

    import org.junit.*;
    import static org.junit.Assert.*;
    import java.util.*;
    
    public class SimpleTest {
    
        private Collection collection;
	
        @BeforeClass
        public static void oneTimeSetUp() {
            // one-time initialization code        
        }

        @AfterClass
         public static void oneTimeTearDown() {
            // one-time cleanup code
        }

        @Before
        public void setUp() {
            collection = new ArrayList();
        }
	
        @After
        public void tearDown() {
            collection.clear();
        }

        @Test
        public void testEmptyCollection() {
            assertTrue(collection.isEmpty());
        }
	
        @Test
        public void testOneItemCollection() {
            collection.add("itemA");
            assertEquals(1, collection.size());
        }
    }

Given this test, the methods will execute in the following order:

    oneTimeSetUp()
    setUp()
    testEmptyCollection()
    tearDown()
    setUp()
    testOneItemCollection()
    tearDown()
    oneTimeTearDown()

(Continued on next question...)