Unit Testing Java Programs | Junit

Enter JUnit
The Round class
Collecting your test cases

Enter JUnit

JUnit is a Java open source project which offers an extremely useful framework for unit testing. If you use JUnit the code above can be written like this:

assertEquals(0, c.parUpToHole(0));
	assertEquals(8, c.parUpToHole(2));
	assertEquals(72, c.parUpToHole(18));

This is much more to our liking. And JUnit also gives us a better error message when a test fails. If we, for example, changes the "72" in the last line above to "71", JUnit will give this message:

There was 1 failure:

1) testSomething(hansen.playground.TestCourse)
	expected:<71> but was:<72>

So now we also automatically get the calculated value of the expression "c.parUpToHole(18)".

JUnit offers a lot of features, but in the following examples I'll show the most common and simple among them. If you are interested in digging into the many options of JUnit www.junit.org contains links to several articles.

In order to make use of JUnit's features we must of course be prepared to follow a set of rules. Briefly these are:

  1. Put your tests in a class that extends the JUnit-class "TestCase".
  2. If your test cases use some common data then set it up in a method called "setUp".
  3. Place the testcode (e.g. calls to"assertEquals") in one or more methods having names starting with "test".

The code needed to make the three tests above will look like this:

package hansen.playground;
	import junit.framework.*;
	public class TestCourse extends TestCase { 
	  private Course c;
	  public TestCourse(String name) {
	  protected void setUp() { 
	    c = new Course();
	    c.setName("St. Andrews");
	    int[] par = {4,4,4,4,5,4,4,3,4,4,3,4,4,5,4,4,4,4};
	  public void testSomething() {
	    assertEquals(0, c.parUpToHole(0));
	    assertEquals(8, c.parUpToHole(2));
	    assertEquals(72, c.parUpToHole(18));

Note that we import the JUnit framework--available for download from www.junit.org. The "setUp" method has a counterpart: "tearDown", that can be used to release resources allocated in "setUp".

The TestRunner tool

To run such a test program JUnit offers the TestRunner tool. It's of course written in Java. It can either be used as a batch tool directly from a command line, e.g.

java junit.textui.TestRunner hansen.playground.TestCourse   

Or you may use the AWT or Swing interface:

java junit.awtui.TestRunner hansen.playground.TestCourse 
-- or --
java junit.swingui.TestRunner hansen.playground.TestCourse

which brings up a GUI interface:

To run other test cases simply enter the name of the class and press the Run button.

To automate testing we'll most often like to run the batch interface, and in this case you can invoke it directly from the test program itself, by adding a main method:

public static void main(String args[]) {

The assert-methods

There are a few more methods like "assertEquals" used in the example above--the most important ones are:


Used for


asserts that the two parameters are equal. a and b must be either the same primitive type or both Objects


asserts that a given condition is true


asserts that an object is null

assertSame(Object, Object)

asserts that two objects references the same object