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So in this video we're going to explore

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what test failure looks like in the IDE.

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And that's when a test fails.

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So as we saw in the previous video, when

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a test passes and is successful, we get green,

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but we can also have red as well. So for

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example here, if I simulate an exception being thrown

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and then rerun,

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you can see here we now have red, and the test failed.

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It says the test failed, 1 of 1 test failed. And

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the reason being, is that we have this RuntimeException

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here and this would be a full stack trace

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which would enable you to pinpoint the exact point

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where the unit test failure occurred and the sequence

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of method calls which led up to that test failure.

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Now the reason for this is because we didn't

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set this test up to expect a RuntimeException.

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So JUnit takes the reasonably fair approach

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of viewing an exception which occurs during

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its execution as a test failure.

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However, if you had a test in which you specifically

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wanted to ensure that an exception must run,

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for example supposing, you're testing some validation

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and you're testing the validation routine with

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bad input, then because you're testing the

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validation routine with bad input, you

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would expect that the class that you're testing

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would throw some kind of validation exception

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back out to the user.

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And so in that case you'd want to tell

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JUnit they are actually expecting an exception.

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And you can do this, by using an

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addon to @Test or rather an extra parameter

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to the test annotation which is expected.

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So if you put expected equals under the class,

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then this signifies to JUnit that during that test

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it's expecting that it's going to get a runtime

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exception and that's a good thing and therefore it will

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pass the test. So if I ruin this now

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you can see here the test passes once again.

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Of course this throw new RuntimeException is

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just contrived and we will never put this

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snippet of code inside a unit test.

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Rather this exception will be thrown

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out from the clash of testing.

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But nevertheless I wanted to show you that just to

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tell you about the expected annotation parameter to

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test. Since that's the way that we can actually

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evaluate that we're getting back the exceptions

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that we expect if the API we're testing is designed

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to them back under that particular test case.

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But anyway, now you know about test failure

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and exceptions in Junit, we should be in

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a good position now to move forward.