JUNIT COOKBOOK

When you need to test something, here is what you do:

1. Annotate a method with @org.junit.Test
2. When you want to check a value, import org.junit.Assert.* statically, call assertTrue() and pass a boolean that is true if the test succeeds

For example, to test that the sum of two Moneys with the same currency contains a value which is the sum of the values of the two Moneys, write:

@Test public void simpleAdd() {
    Money m12CHF= new Money(12, "CHF"); 
    Money m14CHF= new Money(14, "CHF"); 
    Money expected= new Money(26, "CHF"); 
    Money result= m12CHF.add(m14CHF); 
    assertTrue(expected.equals(result));
}

Fixture (骨架)

What if you have two or more tests that operate on the same or similar sets of objects?

Tests need to run against the background of a known set of objects. This set of objects is called a test fixture. 

When you have a common fixture, here is what you do:

1. Add a field for each part of the fixture
2. Annotate a method with @org.junit.Before and initialize the variables in that method
3. Annotate a method with @org.junit.After to release any permanent resources you allocated in setUp

public class MoneyTest { 
    private Money f12CHF; 
    private Money f14CHF; 
    private Money f28USD; 
    
    @Before public void setUp() { 
        f12CHF= new Money(12, "CHF"); 
        f14CHF= new Money(14, "CHF"); 
        f28USD= new Money(28, "USD"); 
    }
}

Running Tests

How do you run your tests and collect their results?

Once you have tests, you'll want to run them. JUnit provides tools to define the suite to be run and to display its results. To run tests and see the results on the console, run this from a Java program:

org.junit.runner.JUnitCore.runClasses(TestClass1.class, ...);

or this from the command line, with both your test class and junit on the classpath:

java org.junit.runner.JUnitCore TestClass1 [...other test classes...]

Expected Exceptions

How do you verify that code throws exceptions as expected?

 For example:

new ArrayList<Object>().get(0); 

This code should throw an IndexOutOfBoundsException. The @Test annotation has an optional parameter "expected" that takes as values subclasses of Throwable. If we wanted to verify that ArrayList throws the correct exception, we would write:

@Test(expected= IndexOutOfBoundsException.class) public void empty() { 
    new ArrayList<Object>().get(0); 
}