Tests. Do I really need to add "throws Exception"?

Question

I saw people using "throws Exception" in tests, but I never do. Should I worry? I never had any issues with that. What's the difference?

@Test()
public void test() throws Exception
{
        //Do something
}

or

@Test()
public void test()
{
        //Do something
}

This is a general question, and it has nothing to do with Selenium (or any other specific technology for that matter). Any method can either throw an exception, or handle it. Correct design is usually that general purpose methods throw their exceptions, while specific purpose methods handle their exceptions internally (you can also apply this rule for "lower level" methods to throw their exceptions, and "higher level" methods to handle the exceptions thrown by those "lower level" methods to which they call). — barak manos, May 05 '14 at 14:27
fixed topic and tags. Thanks for the explanation, but I still don't understand if I loose anything by not using this "throws Exception". — casper, May 05 '14 at 14:31
There is nothing to answer here, really. If you show you exact code, then other users may advise you whether you should handle all exceptions internally, handle some of them and throw others, or throw all of them and let the caller of method `Test` handle them. My guess is that this method is "high" enough in the call-stack to handle all the exceptions internally. But it's just a guess, since you do not provide any other information on your code. — barak manos, May 05 '14 at 14:34

score 6 · Answer 1 · edited May 23 '17 at 11:48

If the code you are testing throws an exception, you must handle it in some way. Either by declaring a "throws Exception" in the method signature, or by using try-catch.

If the code you are calling in the method does not throw any exceptions, then you dont need either of those. The compiler will let you know if you need to catch an exception in some way.

Also note that you can do tests that makes sure an exception is thrown, see this answer

score 5 · Accepted Answer · answered May 05 '14 at 14:44

junit will mark a test as being in "error state" if an exception is thrown from that method. For most usecases, this is essentially the same as failing a test (in the sense that a test that completed in error state did not succeed). A lot of test authors don't like the hassle (or the code-uglification) associated with handling checked exceptions.

E.g., Consider a test that should run a couple of methods and assert the end state of an object:

public class SomeTest
    SomeObject so;

    @Before
    public void setUp() {
        so = new SomeObject();
    }

    @Test
    public void TestSomeFlow() {
        try {
            so.init();
        // must catch in order to avoid a compilation error
        } catch (InitExceptionIDontCareAbout e) {
            fail ("init failed");
        }

        try {
            so.doSomething();
        // must catch in order to avoid a compilation error
        } catch (SomeOtherExceptionIDontCareAbout e) {
            fail ("doSomething failed");
        }

        assertTrue ("doSomething didn't work", so.isSomethingDone());
    }
}

Now consider how much cleaner the code looks without exception handling:

public class SomeTest
    SomeObject so;

    @Before
    public void setUp() {
        so = new SomeObject();
    }

    // Any exception throwm will mean the test did not succeed
    @Test
    public void TestSomeFlow() throws Exception {
        so.init();
        so.doSomething();

        assertTrue ("doSomething didn't work", so.isSomethingDone());
    }
}

score 3 · Answer 3 · answered May 05 '14 at 14:33

Functionally, there is no difference. It only means that the compiler wont complain if you throw a non-RuntimeException. Since JUnit will catch any exception thrown by the test method anyway, it does not really matter. However, it is usually considered a better practice to catch the Exception yourself and use the fail method of JUnit, in which case you do not need the throws clause.

Tests. Do I really need to add "throws Exception"?

3 Answers3