Bad form for JUnit test to throw exception?

Question

I'm pretty new to JUnit, and I don't really know what best practices are for exceptions and exception handling.

For example, let's say I'm writing tests for an IPAddress class. It has a constructor IPAddress(String addr) that will throw an InvalidIPAddressException if addr is null. As far as I can tell from googling around, the test for the null parameter will look like this.

@Test
public void testNullParameter()
{
    try
    {
        IPAddress addr = new IPAddress(null);
        assertTrue(addr.getOctets() == null);
    }
    catch(InvalidIPAddressException e)
    {
        return;
    }

    fail("InvalidIPAddressException not thrown.");
}

In this case, try/catch makes sense because I know the exception is coming.

But now if I want to write testValidIPAddress(), there's a couple of ways to do it:

Way #1:

@Test
public void testValidIPAddress() throws InvalidIPAddressException
{
    IPAddress addr = new IPAddress("127.0.0.1");
    byte[] octets = addr.getOctets();

    assertTrue(octets[0] == 127);
    assertTrue(octets[1] == 0);
    assertTrue(octets[2] == 0);
    assertTrue(octets[3] == 1);
}

Way #2:

@Test
public void testValidIPAddress()
{
    try
    {
        IPAddress addr = new IPAddress("127.0.0.1");
        byte[] octets = addr.getOctets();

        assertTrue(octets[0] == 127);
        assertTrue(octets[1] == 0);
        assertTrue(octets[2] == 0);
        assertTrue(octets[3] == 1);
    }
    catch (InvalidIPAddressException e)
    {
        fail("InvalidIPAddressException: " + e.getMessage());
    }
}

Is is standard practice to throw unexpected exceptions to JUnit or just deal with them yourself?

Thanks for the help.

user_1091589 · Answer

Reg: Testing for Exceptions
I agree with "Pascal Thivent", ie use @Test (expected=InvalidIPAddressException.class)

Reg: Testing for testValidIPAddress

IPAddress addr = new IPAddress("127.0.0.1");
byte[] octets = addr.getOctets();

I would write a test like

class IPAddressTests
{

    [Test]
    public void getOctets_ForAValidIPAddress_ShouldReturnCorrectOctect()
    {
         // Test code here
    }

}

The point is when testinput is VALID ipAddress
The test must be on the public methods/capabilities on the class asserting that they are working as excepted

Bad form for JUnit test to throw exception?

8 Answers