JUnit is a unit testing framework for Java. These materials are based on JUnit 4.

Creating and Running a Test Case

Everything in Java revolves around classes. Previously, you’ve seen classes used to implement drivers . For this lab you will create classes used to implement test-cases . To create a JUnit test case class in Eclipse, do the following:

1. Click mouse-right on the package of the project where you want the new class to go.
2. Choose “New”-“JUnit Test Case”.
3. Choose “New JUnit 4 test”.
4. Make sure the package name is correct.
5. Enter the appropriate class name. JUnit test class names must end with Test.
6. Press the Finish button.

This creates a new test case class to which can add test cases, which are implemented as methods. For example, the following case contains two test statements that verify that the boolean expression 1==1 is true, the second that the integer 1 equals 1, and the third that the double 1.0 equals 1.0:

@Test
public void doNothingInterestingTest() {
	assertTrue(1==1);
	assertEquals(1, 1);
	assertEquals(1.0, 1.0, 1e-3);
}

Note that assertEquals() tests of double equivalence require a third parameter that specifies an error tolerance. If any of these assertions fail, then JUnit automatically signals a unit test failure.

A test class is not a typical Java application so you don’t run it as a Java Application. Instead, you run it as a JUnit test case (e.g., by choosing “Run”-“Run As”-“JUnit test case” Eclipse displays a successful JUnit test as shown here:

Here, the JUnit output is show in the panel on the bottom right. Note that a successful test case like this one displays a green bar, on the right, and a list of test cases that it ran, on the left. Because Eclipse allows you to run all of your test cases or a sub-set of them, make sure that when you run your test that all the test cases you expected to run are listed on the left.

Failing a Test

If any one of the test cases, JUnit displays a red bar and an error message on the right. You can jump directly to the test statement that caused the error using Eclipse’s “Go To File” tool (double-click on the error line in the JUnit output). The following image shows the results for a failed test of 1==2.

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