Exception testing

[Pradeep bhatt]

How do I test exceptions using Junit?
[ March 10, 2004: Message edited by: Pradeep Bhat ]

[Lasse Koskela]

Do you mean test your "MyException extends Exception" class, or test that your code throws an exception as expected?
For the former, I usually test only that the stack trace the exception produces contains the pieces of information I expect it to contain (i.e. the most often the description given to the constructor at creation time).
Something like:

public void testStackTrace() {
    Throwable t = new MyException("Foobar");
    StringWriter sw = new StringWriter();
    t.printStackTrace(new PrintWriter(sw));
    assertTrue(sw.toString().indexOf("Foobar") != -1);
}

For the latter:

public void testSomething() {
    try {
        myObject.doSomething();
        fail("doSomething() should've thrown an exception");
    } catch (MyException expected) { }
}

[Pradeep bhatt]

I was talking about the latter one. Thanks for your help.

[Jonatan Romero]

[ this post has been edited to remove the blatant advertising. Please visit the advertisement here ]
[ March 15, 2004: Message edited by: Jessica Sant ]

[Jonatan Romero]

For an example of how you would perform unit testing with Jtest, imagine that you have just written the fol-
lowing Simple class in your IDE and you want to test it.
Simple.java

package examples.eval;
public class Simple
{    public static int map (int index) {
        switch (index) {
        case 0:
        case10:
            return -1;
        case 2:
        case 20:
            break
        default:
            return -2;
        }
    }
    public static boolean startsWith (String str, String match) {
        for (int i = 0; i < match.length (); ++i)
            if (str.charAt (i) != match.charAt (i))
                return false;
        return true;
    }

To start the test, you tell Jtest to run the Generate and Run Unit Tests test scenario. Jtest examines the
internal structure of the class under test, automatically generates and executes test cases designed to
fully test the class's construction, then determines whether each test case's inputs would produce an
uncaught runtime exception. In seconds, Jtest's test cases cover 100% of the class and identify one
StringIndexOutOfBounds exception.
[ Jess added UBB [code] tags to preserve whitespace, check 'em out! ]
[ March 15, 2004: Message edited by: Jessica Sant ]