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In the last lesson we learn how to use a debugger in this lesson we will use debugger to fix any issue

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in the process.

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We're going to learn a couple of things that people learn how to write unit tests using unit.

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And we also look at another cool feature of Eclipse debugger to debug the issue.

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We want to ensure that the programs we write work correctly.

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Some developers rely only on using system not older print statements to verify program correctness but

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doing this is really low tech and is very time consuming.

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You would have to repeat the process every time some logic is changed.

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Similarly you cannot just rely only on using a debugger debugger should mainly be used to identify the

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exact cause.

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Once we are on that issue.

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So the best runtime solution is to use automated uniqueness.

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The benefit is that they are automated Arnalds also repeatable illness.

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These does ensure that any new changes do not break the system so we can say that the main benefit is

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program correctness at all points of times.

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With that we can feel confident about our code and sleep peacefully knowing that we are in good shape

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.

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I'm sure you would agree that this last benefit is really important.

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G-Unit is a popular open source framework that allows us to write automated uniqueness for Djala programs

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that typically use the best individual unit like methods and Gagin a dot org is the official website

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of G-Unit.

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It was originally written by goingback Eric Gama who are well-known authors and have written some classics

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and software engineering feat and Jaman it is well integrated into eclipse.

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Writing a G-Unit best on a desk is as it is referred to in what setting up method input.

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Then executing the method with the input and finally testing the actual output with the expected value

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.

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So let's get started.

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Underwrite a unit task is Villatoro lot of a debugger.

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Some real work before writing our first unit test case.

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Let's look at some new code that has been introduced first as a department class which is a new class

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and it has an instance variable called name which represents the department name.

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It comes along with a getter and a setter and it is initialized in this constructor course class husbanded

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and couple of lessons ago.

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A new way that will call Department has been introduced here which is of pipe Department OK and the

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department variable is initialized in the constructor or here.

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So that department name is a new parameter Department is initialized only if the department name is

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not equal to null.

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So if it happens to be null then the department variable will also be null and there is also a getter

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for the department ready next to that class a new method has been added call and roll.

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It allows a student to enroll in a new course.

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So courses a parameter here.

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And if this method is invoked on a student instance it means that student is trying to add a new course

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and a student is allowed to are only a limited number of courses on all the courses that are added are

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stored and this data structure and road courses which is an idealist.

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And here is the limit.

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So we are checking that the student is not enrolling more than this limit.

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OK so it is course underscore and underscore Lamech which is a static variable and is initialized with

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a rally tree.

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On this method invokes this print method print and road courses which all it does is simply iterates

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over the root causes and Bentz all the courses that the student has registered for.

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So it prints the course name under department name says ghost or department Daut get name on the result

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or get her far enrolled course this variable which is the RL list which is here which is created here

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.

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Don't worry about this generics related BACS since generics is not yet covered.

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Other than that I want to just refactor just rename the student test class.

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Let's go here to refactor rename it to student test drive.

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Let's just do this next.

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Finish.

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So that's how you rename it class going to refactor under your name.

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The reason we want to rename it is because the ESC is that we are going to write in a minute will be

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named the student test.

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That's because that's the regular convention.

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So if we want to test anything in student then the task is a rewrite by convention has to be student

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dust.

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OK it's not a requirement but just a convention.

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That's the reason we are renaming it to student best driver it should be obvious that much of dusting

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happens and development environment as opposed to a production environment.

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That's because in development and Rutman code is being actively dolar and that is called POBox.

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Testing would help in identifying and fixing those bucks on production.

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You would expect to be near-perfect.

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There is no need for any best guesses.

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Mortars are running Vasquez's.

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We're also Edam system resources as to how to execute the code they are testing.

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So typically real code that needs to be deployed is kept separately from Vasquez's when time comes for

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deployment.

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Only the real code is deployed or not the task is this.

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So let's also follow the same practice and create what gets a subsidy.

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Let me just minimize this.

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Let's go here into the project and let's head new.

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To create a news source folder let's just call it best because we are creating test cases.

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Now let's use the same package name here because we are going robustus this class student writing a

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test case for that and it need not be the same package name but convention is to use the same package

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name as the class being tested.

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So let's just go ahead sip package.

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It's the same one.

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Now let's just go ahead and create our unit desk.

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So go into new year after I quicken her G-Unit desk guess it's just call it call it a student test because

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we're creating a test case for a student and that needs to be the name on the package.

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Here is a package name on class under test would be the Student class no hit next.

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And it was all the methods in the Student class and we want to create a test case for this method.

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Also shows the math that's an object class because Object class is the superclass.

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So this is the only method that we want to test had finished.

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It says are G-Unit for a library to go Billy-Bob because it's not yet added but let's do it later in

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a bit just from the best guess that gets created.

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We'll see how that can be done.

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OK.

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So this is the test case that God created automatically and as expected it shows completion errors because

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their uniform is not in the classpath.

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So we need to add that library.

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So let's just call it what it says gives three quick fixes.

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It says you can add this unit for library book I believe but it's true that I know you can see the compression

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errors Mandvi and it got added here so that our libraries in our other JRD under G-Unit for guess if

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you ever want to remote just right click go to belly button Heydari Movember.

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OK now here are the matter that needs to start is and roar and you can see that G-Unit has created this

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desk is called best Android so it always uses this kind of a naming convention best followed by the

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Mathare the method name that GHI that's going to be tested on.

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Here is an on additions and additions.

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We did not cover unpropitious yet but it's simply a moderator data and it does G-Unit that this is this

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particular method is a best guess.

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So if you read this and you were audited SR as an addition as G-Unit that the method to which it is

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attached can be run as a test case to run them at their G-Unit first constructs a fresh instance of

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the class which is the student class this class then invokes the unaudited matter.

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Any exceptions thrown by that test will be reported as a failure if no exceptions are thrown that Destin's

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is used to have succeeded.

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Maybe look at both failure and succeeded.

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And it should be clear and it should be clear to you.

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Now here there is this matter called fail which is a static method in a class called assert which is

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being imported here.

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OK.

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We haven't had Biscoe static imports.

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If possible I might include a separate lesson for that but I think this discussion should suffice too

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.

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So let's start taking borders as it imports all the static members like the static field from the static

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methods in a particular class.

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So I don't think that this is a package.

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It's a class actually and we are importing all the static members from it.

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And the advantage of that is you don't have to qualified the static member using the class name you

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don't have to do a search dogface.

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You can invoke it directly just like invoking any method in the same class.

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OK.

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So that that's the I'd want it you don't have to qualify it using the class me but you must use it sparingly

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.

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That's because it can confuse your readers if you use it excessively.

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It might confuse the readers of your code or you yourself because it's not clear whether you're invoking

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a method in this class or if you are working a method within this class.

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OK so use it sparingly and just go ahead and run this.

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And it says of one failure.

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The reason is because this method is responsible for that.

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What this method means is it just means that the best guess is incomplete and new to selling the dodo

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bird that you need to implement it sooner it's just be some real code here.

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I do a control issue f on what exactly are we testing here.

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We are testing to ensure that student is not allowed to enroll in more than that the limit the max limit

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number of courses.

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OK.

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So should a student should enroll only in three courses.

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So here is how we set up that task is sort of the input.

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So we're creating a student instance here first then we are creating a course instance instance and

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passing for other department and we are doing the method execution.

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So we are in walking the enrollment third installment by passing discourse one variable which is a course

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which is of course.

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And finally we are testing the output though the enrollment there is not retaining anything.

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We are testing.

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There is a change of speed when when this method is getting executed and we are checking that.

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So what are we dusting here.

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We're getting all the courses that the student has enrolled in.

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So we are sort of credence on our list with all the courses that the student has enrolled and we are

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calling the size method of idlest undertows how many courses the student has registered and it should

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be less than the limit that we have.

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OK.

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And guess if if it is less we are good about but if it exceeds then it means something wrong has happened

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.

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Logic has been written in a wrong way and G-Unit would throw an error on it or spread this message.

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Enrollment limit exceeded should never happen.

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So and then we are adding some more courses here.

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Nothing more than that.

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So as Drew is also a method in the class.

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So let's just go ahead and run this.

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You know it says one error failure zero.

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So what is an error what is a failure or is basically some kind of an internal error like a null pointer

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exception or something like that.

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And if failure is something like that's where you're testing some expected value with the actual or

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they are not meeting that is expected is different from the actual and then Junod were throw we would

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say that a failure has happened.

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So what is the error here.

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It says null pointer exception which means that something went wrong.

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This is the stack trace and it's just DoubleClick and debug it using over debugger.

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So let's go here.

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This is a matter where some issue has come up.

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So let's just set up our break point here and let's call our friend debugger tool and test Java.

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And here it stops.

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So the issue is null pointer exception so we don't know whether it is cause is null courses here or

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with of course don't get Department we are displaying the department name.

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So we are saying get Department we don't know if this is not.

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So one of them is null.

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But in this case it's obviously you know if you holler over course we know that it is not.

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No but it could also be know what caused our get Department is obviously not here.

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So but let's just pretend that we don't know and let's try to figure that out.

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So for that what you can do is we can use a new feature of Eclipse guard expeditions where we were test

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expression expression can be coarse expression can be course not good department.

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So let's just see if any of these expressions is not sort of just going to window which says sure you

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hit exhibition's here.

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Yes and it's an expression.

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It's just called this course which is an expression here and it has some value which means it does not

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know.

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So that's not that's not an issue with that.

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Another way to add exhibition is just copy this on our new exhibition and listed there.

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Or you can also do this you can head control shift.

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I mean you do that it opens this pop up and it shows the value.

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Now if you want this to show up in that exhibitions you hit Control shift I one more time.

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And there you go.

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Here the value.

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So that's the null value.

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So when we are in we'll can get name on this Nuddle it is giving us a null pointer exception.

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So we need to fix that and for that we need this kind of a statement.

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So you would execute this system not out statement only if Gore's Target department does not equate

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to none.

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So that's the fix that we need to have.

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OK.

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But what happened when I just we just added this court thought stop in the same debug session we did

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not stop the debug session.

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So we have just added on the fly we have added our fix on the fly.

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And when we saved it controlled went back to the first day first line of the matter.

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OK.

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Now we can test it right.

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So let's just hit her as you just hit her is the industry on it's just hit or is you

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going to G-Unit.

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We actually have some other failure but this one is gone.

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This area is not that it was something else we will figure that out.

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But the main thing as exhibitions are very useful when you have a chain of in locations like caused

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or get Department thought let's say something else get something DOD get something.

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And that is you would you know if there is a null pointer exception you don't know which is which subexpression

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is good but is not.

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So you would you know an inexperienced Dolapo would keep printing each of the invocations here using

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a system not out and we're trying to figure it out.

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But the thing you can do is you can always do this.

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UNDERSHAFT I know whether it's down whether it's in Larnaca.

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Now if it does not matter then you would expand it and you will try for this.

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So there are a chain of indications chain off in locations like if you a call this has a or b b c c

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or d.

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So if you have a chain of invocations then exhibition's who would be perfect.

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OK now let's just go up go back to our unit.

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Let's see what the issue is.

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It says best Andrle.

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It's a failure which means that the expected value did not meet the actual value.

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So let's just click on that and here it is.

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And the last line there is some issue.

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The issue is let's just going to unroll matter here.

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Let's not use our debugger.

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So here the issue is it says less than or equal to cause and No-Limit.

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This should have been less than similar.

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Because of that it was showing an error even when the fault course was added.

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So if you go back to student dust.

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So I suppose the first course that got added and the logic shouldn't have allowed us to added and allowed

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us to add on so when we try to test it it failed and it helped us to fix this logic issue.

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So that's about it.

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That's all I wanted to show.

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So we looked at how to create a test case and we also looked at the new expeditions feature of debugger

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which is very useful when you have a chain of implications and we need to see some value more there

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.

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So that's about it.