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A unit test is a piece of code written by a developer that tests a specific functionality in the code which is tested. Unit tests can ensure that functionality is working and can be used to validate that this functionality still works after code changes.

Unit testing uses also mocking of objects. To learn more about mock frameworks please see EasyMock Tutorial

JUnit 4.x is a test framework which uses annotation to identify the test methods. JUnit assumes is that the all test can be performed in an arbitrary order. Therefore tests should not depend other tests. To write a test with JUnit

Download JUnit4.x.jar from the JUnit website . The download contains a "junit-4.*.jar" which is the JUnit library. To make JUnit available in your Java project you have to add the the JUnit library file to your Java classpath. See Eclipse IDE Tutorial to learn how to do this in Eclipse.

Create a new project "de.vogella.junit.first". We want to create the unit tests in a separate folder. Create therefore a new source folder "test" via right mouse click on your project, select properties and choose the "Java Build Path". Select the tab source code.

Press "Add folder" then then press "Create new folder". Create the folder "test".

Create a package "de.vogella.junit.first" and the following class.

				

					
package de.vogella.junit.first;

public class MyClass {
	public int multiply(int x, int y) {
		return x / y;
	}
}
				
			

Select your new class, right mouse click and select New ->JUnit Test case, change the source folder to JUnit. Select "New JUnit 4 test". Make sure you change the source folder to test.

Press next and select the methods which you want to test.

If you have not yet JUnit in your classpath, Eclipse will asked you if it should be added to the classpath.

Create a test with the following code.

				

					
package de.vogella.junit.first;

import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class MyClassTest {

	@Test
	public void testMultiply() {
		MyClass tester = new MyClass();
		assertEquals("Result", 50, tester.multiply(10, 5));
	}
}
				
			

Right click on your new test class and select Run-As-> Junit Test.

The test should be failing (indicated via a red bar). This is due to the fact that our multiplier class is currently not working correctly (it does a division instead of multiplication). Fix the bug and re-run test to get a green light.

If you have several tests you can combine them into a test suite. All test in this test suite will then be executed if you run the test suite. To create a new test suite, select your test classes, right mouse click-> New-> Other -> JUnit -Test Suite

Select next and select the methods you would like to have test created for.

Change the coding to the following to make your test suite run your test. If you later develop another test you can add it to @Suite.SuiteClasses

				
package mypackage;

import org.junit.runner.RunWith;
import org.junit.runners.Suite;

@RunWith(Suite.class)
@Suite.SuiteClasses( { MyClassTest.class })
public class AllTests {
}

			

JUnit uses a lot of static methods and Eclipse cannot automatically import static imports. You can make the JUnit test methods available via the content assists.

Open the Preferences via Window -> Preferences and select Java > Editor > Content Assist > Favorites. Add then via "New Member" the methods you need. For example this makes the assertTrue, assertFalse and assertEquals method available.

You can now use Content Assist (Ctrl+Space) to add the method and the import.

I suggest to add at least the following new members.

The following give an overview of the available annotations in JUnit 4.x

The following gives an overview of the available test methods:

http://www.junit.org/ JUnit Homepage

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