JUnit test — analysing expected Exceptions [duplicate]

Answer 1

If you want to compare message along with exception type then you can try below code snippet.

    @Rule
    public ExpectedException expectedException = ExpectedException.none();

    expectedException.expect(IllegalArgumentException.class);
    expectedException.expectMessage("Parameter is not valid"); //check string contains
    expectedException.expectMessage(CoreMatchers.equalTo("Parameter is not valid")); //check string equals

Note: This will work for junit 4.9 onward.

Answer 2

I'm not sure if you should. Using a try-catch block to check the error message is so junit3ish. We have this cool feature now that you can write @Test(expected=CriticalServerException.class) and you want to go "back" and use try-catch again to fetch an exception you expect, just for checking the error message?

IMO you should stay for the @Test(expected=CriticalServerException.class) annotation and ignore the error message. Checking the error message, which can be changed a lot as it is a more "human readable" string and not a technical value, can also be tricky. You are forcing the exception to have a specific error message, but you might not know who generated the exception and what error message he chose.

In general you want to test if the method throws the exception or not, and not what the actual error message looks like. If the error message is really so important you should maybe consider using a subclass of the exception it throws and check it in @Test(expected=...).

Answer 3

try{ 
    //your code expecting to throw an exception
    fail("Failed to assert :No exception thrown");
} catch(CriticalServerException ex){
    assertNotNull("Failed to assert", ex.getMessage()) 
    assertEquals("Failed to assert", "Expected Message", ex.getMessage());
}

Answer 4

Use MethodRule as a common solution, if you have many test cases to test

public class ExceptionRule implements MethodRule {
    @Override
    public Statement apply(final Statement base, final FrameworkMethod method, Object target) {
        return new Statement() {
            @Override
            public void evaluate() throws Throwable {
                try {
                    base.evaluate();
                    Assert.fail();
                } catch (CriticalServerException e) {
                    //Analyze the exception here
                }
            }
        };    
    }
}

Then use the Rule to your test class:

@Rule public ExceptionRule rule = new ExceptionRule(); 

Answer 5

Use catch-exception:

catchException(obj).doSomethingCritical();
assertTrue(caughtException() instanceof CriticalServerException);
assertEquals("Expected Message", caughtException().getMessage());