Unit Testing using JUnit
What is JUnit?
JUnit is a framework for testing parts, or units of your code. In general, these units are
considered to be the methods of each class. JUnit can help you to make sure that each of your
classes work as expected. In unit testing you will usually write one test class for each of the
classes that you want to test. Your test class will often include a test method for each method
implemented by the class being tested. But keep in mind that this is not always feasible, or
necessary. A test case will, and should often touch on more than a single method. These tests
should be written to make it likely that when all the tests pass, the code is functioning as
required.
Unit testing is very common when you are doing test driven development (TDD). TDD is a
methodology in which you write the test code first, and then write the code you wish to test.
With JUnit, if you know what classes and methods needs to be in your system, and what their
functionality should be, you can start by writing a set of test cases first, and then fill in the body
of your methods to pass those test cases later. And when you later need to change your code,
the test cases can be a great help in making sure that your code stays robust and relatively bug‐
free.
Basic Information
Before you begin, we would like to call your attention to the following conventions:
A Test Case Class is named [classname]Test.java, where classname is the name of the class that
is tested.
A Test Case Method is a method of the Test Case Class which is used to test one or more of the
methods of the target class. Test Case Methods are are annotated with @Test to indicate them
to JUnit. Cases without @Test will not be noticed by JUnit.
JUnit assertions are used to assert that a condition must be true at some point in the test
method. JUnit has many types of assertions. The following is a selection of the most commonly
used assertions:
assertEquals(expected, actual): Assert that expected value is equal to the actual value. The
expected and actual value can be of any type, for example integer, double, byte, string, char or
any Java object. If the expected and actual values are of type double or oat, you should add a
third parameter indicating the delta. It represents the maximum difierence between expected
and actual value for which both numbers are still considered equal.
assertTrue(condition): Asserts that the Boolean condition is True.
assertFalse(condition): Asserts that the Boolean condition is False.
assertNull(object): Asserts that an object is null.
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