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[No Audio]

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In this video, we're going to explore

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JUnit's @Before annotation, which lets us

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keep our unit test setup code dry.

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That stands for don't repeat yourself, in other

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words, we don't have the duplication of a setup

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method, and we'll see how to do that right now.

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So let's think back now and look at the unit test

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and assess the kind of unit test that it is.

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So thinking about that test we've written, because

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that's obviously a very simple test and we don't

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usually have methods which are so simple,

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they're just a simple function which is defined

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as a static method taking two integers.

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Normally we have state on objects.

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So let's rework this production class just

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for the sake of our example. And let's

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assume that it isn't a static method. In other words,

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we have to create some instance of Calculator first.

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It's like we go back to here.

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We can see this is highlighted in red.

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This is now a compilation error.

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It can't reference from a static context.

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So we could fix it by doing this new Calculator.

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However, that violates our Arrange/ Act/ Assert

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sections because the test object, the object which

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we're testing is the system on the test that

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needs to go into the arrange phase.

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So let's just put it in the arrange phase instead,

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just to keep things nice and consistent

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with the methodology.

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So now just rerun that, just to make sure

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everything still works, which it does. That's fine.

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And let's suppose we had another test.

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Just copy this one for now,

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just click testAdd 0.

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So a test when we want to, see

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what happens when we add 0 to something.

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Not the most interesting test, but we

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don't care about that for now.

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We just care about learning about how JUnit works.

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So, this should be the answer here,

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lets just make this a bit more descriptive.

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testAddPositiveNumbers,

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testAddZeroToPositive

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and rerun this now, if I do run CalculatorTest,

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you'll now see there are two

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tests which have been run here.

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So now there are two test cases on this

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test class, and every time you click a test

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method, any output related to that test method would

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appear here, or any test failure.

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For example, assertions not passing that kind

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of thing would also appear here.

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If had a full set of test methods, say 20

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test methods here and say like three of them failed,

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then you'll be able to click on the individual failures

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and see what happened in the right hand pane here.

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But what I want to show you now and

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highlight is the fact that we have some duplication.

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So here you can see when we're arranging, either

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of these tests, we do the instantiation of the

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system of the test in the method each time.

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So we can refactor this slightly and

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we can use another one of Junits

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annotations, which is called @Before.

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So if I now use @Before again from org.junit

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and have a method public void setup.

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This will enable me to put this setup card

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in that method,

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delete this one

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and this method will be executed

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before each test, just set up the so called test

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fixture for the test and that basically means the set

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of objects or the state if you like of the

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test class before each individual test is run.

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Now you can see here this is in red, it's

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calc in here and here and that's because we need

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to actually push this state

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business system and the test that we're going to be

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running a test for, into the test class itselfs

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so we give it a private member

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variable here, which we can call calc.

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And now if we rerun

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all the tests again they should be green,

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so this is nice this basically means that

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we've got, commonality to set up our test fixture in

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this setup method, so it's not duplicated across all of

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the tests and we have individual arrange sections

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which are very specific to each test so this is going

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into being a very nice kind of well structured test.

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Now it doesn't look like much at this stage because

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this is a very trivial example. But if you imagine

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you had a class which maybe takes a few different

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collaborators a few different objects which it needs to

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interact with, and maybe they need to be set up in

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a specific way which is common across all these tests.

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Then you can imagine it, this this method would be

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quite useful. And that's how we can keep set up test

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code dry using the @Before adaptation.