JUnitQuickStart.adoc

JUnit Quick-Start guide for Eclipse

1. In Package Explorer view, click to select the project where you want to add a test

2. Use File> New to create a new source folder called test

3. Click to select the class that you want to test (Known as Class Under Test or CUT )

4. Use File> New to create a new JUnit Test Case as follows:

   • Choose New JUnit 4 test (not JUnit 3)

   • Source folder: The test folder that you created above.

   • Package: Same as the CUT

   • Name: Your test class should be named as per your CUT followed by a suffix of Test eg DogTest

   • Probably tick to create setUp() method

   • Press Next and optionally tick to generate test methods

5. Then run the test class by right-clicking it in the Package Explorer view and choosing Run As > JUnit Test

6. The code in your test methods should be as simple as possible (complexity requires tests and we don’t want recursive hell!) The three essential elements are Setup Invoke and Verify eg:

   Dog myDog= new Dog();	// Setup
   myDog.eat( 10 );		// Invoke
   assertEquals( 17, myDog.getWeight() );	// Verify

Further steps to research and try

1. As an alternative to the Eclipse wizard, code your test method manually, such as:

   @Test
   public void testNewPerson_negativeAge_throwsException() {
     ...
   }

2. Where there is common setup code we can remove it from the test methods and place it in the @Before method, which is called before every test method gets invoked. Similarly the static @BeforeClass method which is called just once, before any of the test methods are invoked.

3. Where the verify logic becomes complex, this can be simplified by using the Hamcrest library eg:
   assertThat( i, anyOf( greaterThan(j), lessThan(k) ) );
   Hamcrest requires static imports, which some IDEs cannot generate automatically, eg the above code requires:

   import static org.junit.Assert.assertThat;
   import static org.hamcrest.CoreMatchers.anyOf;
   import static org.hamcrest.number.OrderingComparison.greaterThan;
   import static org.hamcrest.number.OrderingComparison.lessThan;

4. If you need to check that a method threw an exception, research the optional parameters for the @Test annotation, such as:

   @Test(expected=IllegalArgumentException.class)

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Happy hacking!

Mike [dot] Burton [at] MycoSystems.co.uk