如何在jUnit测试中强制方法引发异常？

Question

Actually this is for code coverage and I'm having a hard time, covering to catch statements. Any ideas?

for example:

I want my selectSomethingBySomething() method (which selects from db) to throw an SQLException which is pretty hard on a test method without actually touching the actual source code. Given also the constraint that what I can only control is the parameters for the WHERE clause.

Answer 1

You need to first mock the class containing selectSomethingBySomething() and then record this behavior. In mockito you'll say:

SomeDao someDaoMock = mock(SomeDao.class);

willThrow(new SQLException())).given(someDaoMock).selectSomethingBySomething();

Then inject someDaoMock into your class under test and when it calls someDaoMock.selectSomethingBySomething() it'll throw previously chosen exception.

Answer 2

You need a mocking framework like Mockito. Check out the easy-to-read refcard here:

http://refcardz.dzone.com/refcardz/mockito

Answer 3

Using EasyMock you can mock an Class and the method calls of that particular Class.

For example:

If DoSomethingDAO is the ClassName,

Mock the class like DoSomethingDAO mockDAO

EasyMock.createMock(DoSomethingDAO.class);

now that you have to mock all the calls that are being made from this mockDAO.

if the method returns a value we need to mock the call like below.

EasyMock.expect(mockDAO.selectSomethingBySomething()).andReturn(EasyMock.anyObject());

If the method throws an exception below is the method call

EasyMock.expect(mockDAO.selectSomethingBySomething()).andThrow(new (typeofExecption));

for void methods

mockDAO.selectSomethingBySomething();
EasyMock.expectLastCall().atleastOnce();

Answer 4

There are lots of ways do it, but my advice is don't aim for 100% code coverage. It simply isn't worth it. You're making life difficult for yourself for negligible benefit.

However, if you really want to test it, probably the best way is to alter your code to make it more testable. Make your data-access class implement an interface, then use a mocking framework (such as JMock) to mock it out and throw a SQLException. (You can mock concrete classes but that is frowned on.)

Answer 5

You actually do not need an additional Framework to do the Trick. Here is how:

    Exception hasToBeThrown = null;
    try {
                 methodThatShouldThrow();
    } catch (Exception e) {
        assertTrue(e.getMessage().startsWith("if you want to...")); // JUnit will miss this, if not thrown, so we need more
        hasToBeThrown = e;
    }
    assertNotNull(hasToBeThrown); // but this will do