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Hey everybody has gone this Caleb with their slopestyle.

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And in this video we're going to continue unit testing.

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But this time we're going to be actually testing the server basically that our images are housed on.

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That's not our API it's not our server.

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But the cool thing is that we're going to be able to create a mock of you r l session and basically

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a mock is going to allow us to create an imitation our own version of your Else session but we'll be

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able to actually create it and slim it down basically to the most primary components that we actually

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need to test.

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And it just gives us access to it in a much easier way than needing to use the entire You are all session.

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So pull up your project and what we're going to do is we're actually going to create another file in

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the helper's folder called download client.

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So go ahead and right click click new file and then it's just going to be a basic swift file called

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download client.

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OK.

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Now create a class and name it download client Calixto.

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And what we're going to do is we are basically going to put one function and it's going to look familiar.

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It's going to basically be this same function download image with your URL so phunk download image with

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you r l u r l of type string and we're going to go ahead and basically set our your all to instead of

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just being a string we can change it to.

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And actually r l by typing guard let u r l equals u r l from string and we can pass in that r l string.

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Else we're going to go ahead and just call fatal error.

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And now we have a u r l of type u r l and now we can do is we can basically perform our day to task

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where we pass in the U R L and we get no data response and an error at the very end.

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Just like you are l session.

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But the thing is we don't have a session we don't have a u r l session but we need to make a mock u

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r l session and we're actually going to go ahead and create a variable called session of type u r l

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session and it's going to be equal to u r l session shared.

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Now inside our function we can call session data task and we can pass in our u r l here and we can push

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enter on our completion handler there and type in everything we need like data response and error.

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And then at the end we'll just go ahead and erase the code in there for now.

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And of course at the end of a day a task you need to resume's so that it actually completes and it knows

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when it's done.

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So basically we have a function that we pass a u r l into.

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We create an actual u l instance we create a data task from our session here.

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And then you know we call resume at the end so that it actually you know does what it's supposed to

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do and here will be code to create image.

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So if we try to build this you'll see that everything works.

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It builds successfully.

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The code is good but basically what we need to do is we need to test this.

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And so we're going to go ahead and right click click new file and create a unit test case class called

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download client.

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Client tests go ahead and save that.

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And then what we're going to do is we're going to get rid of all the beginner boilerplate stuff.

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We're going to import our project here by typing testable import photo load just like we have been.

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And then what we're going to do is we're going to go ahead and basically create an instance of our download

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client by typing var such as of type download client and then we're going to go ahead and set it up

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in set up.

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So go ahead and type the system under test is equal to download client and instantiate it.

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Then when we tear down we're going to say sut equals nil like so.

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So very cool we now have our download client setup in our test or in our test case.

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But what we need to do is we need to write a test and we're going to actually just as an example I'm

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going to show you how you should test your API to make sure that you know you're using the expected

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host and using the expected paths for particular endpoints.

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It's really really helpful.

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And you can actually do this even before the API is done.

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If you have an idea of what the API will be like you can do this before it's even up because we're actually

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just using a mock or else session.

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So let's go ahead and write this test funk.

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Funk.

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Test download.

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And we're testing to make sure that it uses the expected host.

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OK.

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Now what we are going to do is we're basically going to take our image you are l.

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We're going to call our download image function from our download client and we're going to go ahead

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and basically pull out your old components and then verify that the moral component for host is equal

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to images dot pixels dot com because in our helper's you'll see that is the host from our images we're

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going to make sure that it's actually using the right host.

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So go ahead and type let image you r l that's going to be equal to image or L strings.

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And we're just going to pull out the item at the third index because that's the image we've been using.

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Then we're going to call the set system under test download image with you are l we can pass in our

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image you are all there.

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And now we can actually create an instance of your elso guard let your L equals you r l from string

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K like so and we're going to pass in the image you are l.

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Otherwise we're going to call ex-city fail since we're in a test and then return.

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OK we've done that before.

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Next we're going to go ahead and create the components from this u r l.

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So Type let your L components equals u r l components and we can basically use you r l k.

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And we want to resolve against the base you are l.

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That's true.

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So what we're going to be testing for is equivalency so X-C assert equal and we're going to check your

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components.

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Host K because we're checking to make sure that the host is equal to what it's supposed to be.

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And if you remember it should be images dot pixels dot com.

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So if I run this this test should pass.

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But the interesting thing is that we have not actually properly set up a mock your L session.

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And so we're going to do that now.

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And so we're going to extend our our download client tests and we're going to basically create a new

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class called mock you are all session.

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So go ahead and type extension download client tests.

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OK.

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And we're going to go ahead and create a new class called mock session and it's going to basically have

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a couple of properties you know one that we need the most is yourself so type var you are all that is

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of course of type you are l and it's optional because it's not you know given a value until it's initialized.

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And so then what we're going to do is we're going to go ahead and recreate the function data task with

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you r l so type phunk data task with you r l of type u r l and then we have a completion handler which

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is escaping and of course we have data.

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We have a moral response.

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And we have what is it an error I think.

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And then of course the return there is void and the function itself data task returns a your L session

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data task can't.

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So there's that.

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And then what we're going to do is when this is called we're actually going to set self your L K for

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the session.

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We're going to set that to be equal to whatever you are l we pass in when we call data task.

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OK so then the session then has a u r l initialized.

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And then what we're going to do is return your L session shared data task whoops data task with you

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Earl.

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And we can pass and the u r l from r u r l session.

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That's how that's going to work.

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So if we build this it's going to go ahead and go away the errors.

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And now we have what is called a mock u r l session.

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This is basically your L session but with the function that we're actually testing and the only property

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that we really care about.

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So that's what's cool is we can basically create a smaller much much easier to test version of your

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session to make sure that it's working the way that we want it to work.

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Now this might seem silly but basically we're testing to make sure your L session works.

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You know but Apple built your L session so we're basically going to create our own to make sure that

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it's working the way we want in our particular use case.

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So there are a few things that we still need to do what we need to actually do is to make sure that

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when we use our mock you are all session that it's actually able to access this function from your session

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and the way we can do that is with a protocol so we can go ahead and type protocol session protocol.

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That's what we're going to name it.

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And the function we're just going to basically take the function that we wrote here.

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I'm going to copy it and then paste it in K because that is the function we are passing and you are

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l.

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We have our completion handler and that is the protocol that we need.

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And if we conform to this protocol our mock you are l session should be able to conform to it as well.

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So go ahead and create an extension of your Else session.

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OK you Arel session and we're going to conform to the session protocol.

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OK very very cool.

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Now since this function is already a part of your session we don't need to actually type it in the extension.

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We can just go ahead and leave it as it is but where it definitely becomes important is in our mock

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you or all session.

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So go into your download client tests and what we're going to do is in order for mock your session to

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successfully utilize this data task function we're going to go ahead and conform to session protocol.

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And now we have access to this basically we've conformed to the protocol because we have added in data

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a task and you know what.

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If I were to actually get rid of this it would tell me that I'm not conforming to the session protocol

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in just a second it will get there.

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It'll tell me hey there we go OK.

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Undeclared use of type session protocol.

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And if I go down here I can call a to task and there it is there is our function and we can paste our

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code back in here self-doubt you are l equals u r l and then return or session Scott shared dot data

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task with you l and pass in the L U r l.

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Cool.

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So we are now conforming to that mock are Session now is actually accessing the proper function from

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your session which is very cool.

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And basically we can now use this as the actual session that download client uses.

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So in download client go ahead and set up the session here not to be your whole session but instead

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to be Mach. you are all session.

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But what happens when I try to build that it's going to say hey you don't have access to that here.

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So what I can do instead is set this to basically conform to session protocol because it's going to

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be able to access either our mock you or all session or an ordinary session.

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But since we're using it with a mock your all session it's going to use that.

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So very very cool.

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That is now setup we can now go back and modify this to fit our needs a little bit better.

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So in our tests we're going to go ahead and set our client here to have a mock session and so we need

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to go ahead and create one mock you or else session of type mock your session.

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Then we need to set it up and initialize it.

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Mock your all session equals mock all session and then check it out.

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If I type s u t dot session I can set it to be our mock u r l session then we can use our own little

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mocke and this is really helpful for things like for libraries that are just really really big that

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have a lot of different functions and features and abilities.

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You can basically strip it down and test only the features and functions that you really need.

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And so we now have set our download client to have a session of our own maake which is perfect and you

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can basically mockup anything you want to make sure that it works the way that you're hoping.

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And now if we go ahead and run this it's going to use our mock or else session that's conforming to

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the session protocol that we built and it'll test it.

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It'll run and it looks like our test successfully pass.

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Well at least most of them did.

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Now all of them did.

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OK.

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Very very cool stuff.

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So let's go ahead and let's write one more test here.

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Before this video will be over and we're going to just make sure that our test when it downloads an

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image that it's actually using the expected path because we have our host is good.

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We would use that to check that our API is you know is working properly.

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Make sure that our app is pointing to the right server and then we're going to make sure that it's using

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the expected path.

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So I just copied the test from above and I'm going to change this to uses expected path and the only

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thing I need to change is the U R L here instead of using the image u r l.

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I'm going to go ahead and actually write in a custom u r l here.

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So yes colon backslash backslash.

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And of course we know our host is images of pixels dot com.

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But then if you look at the you or else here the path in order to get to photos is photos.

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So we're going to go ahead and add that slash photos and basically that is going to be the L that we

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are testing.

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We're going to go ahead and check to make sure that your components drop path is then equal to slash

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photos.

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OK so all that we create We're going to make sure that it's actually pointing to the proper photo path.

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So let's go ahead and let's build that so our diamond comes up let's click and build it.

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Make sure that it actually runs and succeeds.

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And we're going to basically check to see if it's using the expected path and look at that.

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It is.

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So that is amazing.

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Very very cool stuff.

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We have now basically created a mock session.

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It is a mockup or an imitation of your L session that has the property you are l that we needed.

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And it has the function data task Kaina.

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Of course this is not all session you are all session if you go into here and into your session you'll

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see there is a lot of functions lots of capabilities of your L session.

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But we don't need all those We're only testing the data task feature and so we built our own custom.

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Whereas it now we built our own custom.

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Mark you are all session with all the stuff we needed which is really really really cool.

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This is great for testing things that you don't own you can create your own I guess instance of them

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and link them with the protocol which is very very very cool stuff.

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So let's head over to the next video where we're going to continue learning about unit testing.

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I'll see you there.