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This what's up and what the price as does Snopes dot com.

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And in this exciting video we are going to create the logic for the application or the math that does

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the calculations and sometimes this is called The business logic if you look up programming definitions.

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Business Logic is the code that basically does the thinking and that code is very important and needs

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to be tested needs to be well-written.

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And so what we're going to do is we are going to create the not only the code to do the math we're asking

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to write a unit test your very first unit test so it can be well tested and trust me.

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If you have any type of unit tests in your project when you are applying for a job if you're doing an

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example project you will get a thousand more points than the other candidates who do not have unit test.

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It's very important to companies so this is a good thing to start learning right here right from the

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beginning.

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So what we're going to do is we're going to select our just look at your project up here and then we're

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going to go to Ed. at Target.

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OK.

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And we're going to add a unit testing Bunuel now.

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Before I do that if you created your project with a testing bundle it'll be right here ready so you

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know when you create a new project and if you want to do unit tests or you itas We've had ours off.

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But if yours is on then you don't need to do this step but I'm assuming that you've done the same thing.

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I haven't heard of turnoffs So we're going to go to editor at Target and we're going to add a U.S. unit

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testing bundle and we're going to say window shop retests.

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Great great great.

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All part of this project.

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Wonderful.

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Awesome.

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So now we have unit test as you can see in this folder here.

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We have some functions for us here.

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So that's great.

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So the next thing to do is actually create some code.

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So here in the windows shopper I'm going to create a new group and we're going to call this model and

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what we're going to do.

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We might.

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So we might have had this code let's say in a model file on a wage model.

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It's a small app but it's fine.

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So in this model file We're going to do a new file.

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It's going to be a swift file and we're going to call this wage for lack of a better term.

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We would assume maybe in the future would add more logic here.

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It's going to create this wage.

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And what we want to do is create a class called wage.

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And inside this class we're going to create a class function class funk.

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And what we want to do is create a function that will basically take inputs and then produce an output

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basically the math behind this if you can think about it is we take the price of the item and we divide

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it by your hourly wage and that's going to tell us how many hours that you need.

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And so we want to write a function that does that for us.

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OK so we're going to call this get ours.

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All right.

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I'm going to say for wage to say wage and swimmy of type double.

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And then we're going to say and price right now the price the Colon's can be here and of type double

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and we're going to return an integer you know because that's the that's the number that says 14 hours

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15 hours.

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We don't want to say fifteen point five hours because we just want solid numbers.

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OK.

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And we're going to return it.

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All right.

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Now maybe you are seeing some new things here.

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OK.

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Hours for wage why do you have.

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Why do you have to parameter names here.

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Well what I have here actually is a parameter name.

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And then the variable name itself.

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So this is more for autocomplete when you're typing in things you can see a readable description if

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you like.

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All that makes a lot of sense.

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And this is the actual variable that you use.

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And so you can actually name your parameters like so and this indexes the parameter name space and then

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the variable name with the colon and then the type.

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OK so get ours and what we want to do is we want to write code to get the appropriate hours.

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Now I'm not going to be doing test driven development here where you do want thing you felt you another

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thing I felt I'm going to write unit tests the way I write it and most people I know write them which

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is you build it out and then you test it.

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OK.

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And so remember we talked about the math.

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It's basically price divided by wage.

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But ours is a unique circumstance.

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So let's let's do some math here.

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Let's say we have an item that's $250 and move this up here $250 and 53 cents.

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And let's say we make $15 an hour or 15 50 an hour.

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OK.

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So that's saying you need to work sixteen point sixteen hours.

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Well that's confusing where we don't want to.

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We're just trying to make a purchase decision we don't want to calculate mid hours of what we actually

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want to have happen is we want the result to be 17.

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OK.

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Because we know 17 hours guarantees the purchase OK.

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And it's cleaner and easier to read and that's the logic that we want.

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So what we want it what we don't want to end up doing is we want to round up whatever the value is we

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want around up to the next whole number.

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Okay.

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And so we need to write the logic for that as well too.

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So we would do the division math and then we round up to the next whole number so we can guarantee that

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if we work this many hours it pays for it and you might have a little more left over but that's ok.

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I think that calls for a better user experience.

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And so it's pretty simple actually.

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So we just say return and what we're going to do is we're going to say seal this is math ceiling.

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So it's going to go up to the next level.

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So if you give us 15 50 it would go up to 16.

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Okay.

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And we're going to say price divided by wage.

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Right.

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So that's what we want.

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But the problem with this is it's going to return a double k cannot return double the type int.

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And remember the application costs for an integer because that's what we're showing to the user.

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So this is easy enough we'll just convert it to an int when it's done.

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So in like so.

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And the good thing about this is if it's like even five point zero it or get rid of the zero and just

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converted to an integer which is exactly what we want.

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So that math is not that hard but let's go and write the unit test for now to ensure that it's giving

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us what we want.

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OK.

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So what we're going to do is we're going to go into our window shopper tests and let's just put a function

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in here I'm going to say phunk or just say test wage or get our test tests wage for hours test hours

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which said tests get hours.

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So I'm going to say OK and all we want to do is run some tests to make sure that our code is actually

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working correctly.

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We read in the code we think it works correctly but how do we know for sure.

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So it's pretty simple.

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We're going to use ex-city assert and I'm not covering everything in unit tests.

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I'm just covering what we need to know for this application.

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So ex-city assert and you can assert true or false.

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We're just going to say X-C to you sir.

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And then pasand an expression because it's just easier for this example.

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And so what we want to do is we want to call this wage function.

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So wage get hours and remember this is a class function.

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So you don't have to create a copy or an object of wage to use this you just wage Dopp then the function

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name.

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And this is only one function in memory that every instance of a wage is going to use or you can access

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from anywhere.

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So in here I should be able to type in wage Daut but not at home nothing's coming up.

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So because we added the unit tests later on in the project our code files don't recognize that target.

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So we need to do is actually go over to our wage file here and open up the right hand side here and

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see this little file that's highlighted here.

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This is called the file inspector.

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Now you have to do is click this target here window shopper tests and it will now let you test and have

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access to this wage file.

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So now if I go back to window shop or tests I can say wage dot hours and it's now available so we can

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start passing in numbers here.

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So what I can do is I can say for wage so let's say we were making $15 an hour actually make it easy.

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We'll say $25 an hour and the price is one hundred.

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So we should assert that the result we get is equal to 4.

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OK.

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So right because 25 and 200 is for maybe using it.

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But Mark we did the ceiling thing where it goes up one well it only goes up one if there's a decimal.

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This is this is zero right.

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So 25 to 100 is for without any remainder so this should be for for sure.

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Let's the one with numbers.

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Now what we can do is we can actually run some math here so we can actually run this one right here.

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So let's copy this Kamensky and I'll delete it here in a second so we can run another assertion accede

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to assert let's say wage that get ours for wage.

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And so let's say the wage is 15 50 and the price is two hundred and fifty.

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Fifty three by command space again remember sixteen point sixteen.

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So using the ceiling function this should be 17.

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That's the value we're looking for in our function.

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If it comes out true and this works it means that we rewrote the correct code.

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So this should be equal to 17 because of the ceiling function which makes it go up by 1.

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So this should be equal to 17.

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All right.

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So what we just done here is we've just written a few tests.

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We've met we've passed the numbers here so this is how unit testing works.

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You you you call a function and you pass data and you get data back.

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That's good code.

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Good code is when you pass and parameters and get things back.

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Bad code is when you have a bunch of functions that depend on other functions that's called function

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dependency and it's very very bad.

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Functions that depend on other functions is bad.

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Let me say this again this is a protip.

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OK.

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When building your business logic functions that depend on other functions is very very bad.

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You want the modularized.

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OK you don't want them to rely on anything.

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So you passed data in and they spit data out and that is that's perfect.

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It's called functional programming and that's the way you want to build your applications and so we

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are testing that.

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If we pass in a 25 and a 100 that we get a 4 it's going to assert that otherwise it's going to fail.

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And then in the second case we're asserting that this decimal value this way it's 15 to 50 and the price

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is equal to 17 that it rounds up.

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OK and let's make sure.

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So point 16.

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You know normally if you were doing that of around a function with around down around.

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But we know that it's covering all of our bases because this is below point 5 and still rounding up

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to 17 or so we think.

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So I think these are two tests and I think there are enough.

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What I'm trying to say.

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I think we have enough tests here and I need to do to actually run your function here or your unit tests.

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Click this little icon right here.

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So click the play button on it.

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It's going to build it and then it's going to run it.

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You always always always want to run tests before you run your code.

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So in other protip always run your tests before you run your code every single time.

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Test run your tests before you run your code.

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That way you ensure that you haven't broken anything and it's testing as you can see up here at the

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top and it says tests has succeeded.

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Hooray.

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And if you're absolutely new to unit testing maybe you're thinking Mark I really don't understand the

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point of this.

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Like I really don't like my is good so why do I need to test it.

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Well here's a perfect reason why.

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OK here's the perfect reason why so let's go on to the Google and let's type in Iowa development round

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double OK.

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I'm just grabbing a random stack overflow.

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Let's let's use Swift actually 2011s still up there in the rankings.

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OK running a double double blah blah blah blah blah.

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OK.

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So interesting.

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So you can round a you can use around.

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OK that's that's an actual function you can run a swift and you can round something right.

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And so my point in showing you this that you could go on to stack overflow is because there's multiple

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ways you can do things you can round stuff you can call DOT rounded and all you can do all kinds of

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things.

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And so my point is there's multiple ways of accomplishing something so let's say you wrote this beautiful

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code and it works OK.

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And now you've just hired another developer or you're working with a buddy and he comes in and he's

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he goes to your wage function and he's like you know what does this seal thing this doesn't make sense.

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I don't think that's what we want.

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So what he does is he says I think it be better if we use the round function.

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OK.

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Like so and then we go ahead and pass in price divided by rage.

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Let's say he says this because I think this is a much better solution.

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And then he commits.

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He doesn't even tell you about it.

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Right.

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Well.

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Well let's go ahead and go back to our unit test.

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Your bro has just messed with your code and browes never do that.

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Dude if your bro is messing with your code he's probably not your bro.

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You need to find a new bro because he's not a coat bro.

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And let's go to a window shop or tests and what we want to do is run it again and see what happens.

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So it broke.

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What in the world.

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It broke what's going on here.

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This is really interesting.

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So our unit tests just saved our life so let's go take a look here.

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What I want to do is I just want to I want to print this here

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see if it will let us or if we have to put it inside a string.

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I want to print this here.

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Let's see if it will work now.

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You wanted in a string that's fine.

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No big deal.

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We'll use some string Interpol lation like so I would just pass that industry.

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So what it does I just put a print statement in there and let's just run the tests and see what happens

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so running the tests.

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Well we should see a couple of prints.

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Okay perfect.

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So a 4 and then a 16 is what we got.

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But wait a minute wait a minute.

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16 but we want to 17.

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Our logic called for 17 and we got to 16.

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Well it just so happens that the round function if it's point four 9 or lower rounded down if it's point

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five or higher it rounds up around it to 17.

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Only if it was point five or higher so our bro just broke our logic.

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And if you did not have that unit test you might never know you might have published a few versions.

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And some people are like hey I think your apps broken because I work 16 hours and it wasn't enough money

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to buy the thing you're like.

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Well why not.

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Because he needed some change.

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You never rounded up.

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And so you just created a terrible user experience because your bro came in and messed with your code.

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But if you had unit tests and if you you're running them every time.

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Like we just did you would know that it's broken.

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Teske our So what you do with the unit test is you test out the desired result which in our case was

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17 the Foresta worked but the 17 did not.

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So we knew that we knew that something was wrong right out the gate.

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So basically here's the here's the scenario.

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Let's say you made 10 changes your bromate 20 changes and you're about to go to version 2 and publishes

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the after.

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But first you're like I'm going to be a good developer and run all my tests in your run.

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And it breaks.

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And then you come to find out that your bro messed with your code and now you can make a decision you

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could fire the guy or at least yell at them.

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Don't buy him any food at least for sure.

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And then also you can go in here and you can fix the code.

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So that's the value of unit tests.

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You run the tests and make sure nothing in your code is because stuff changes especially if you have

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like five or 10 developers working on a project.

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Things can change.

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So luckily we had our test to let us know that it's broken.

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You never ever ship with any red Xs.

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OK.

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So protip never ship code with the red Xs K or never ship code that with failing unit tests because

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you know something is wrong.

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So now we can go back to our wage and we can put it back the way that it was supposed to be OK.

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That's the value of unit tests.

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Very very powerful.

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So we know our codes are working and we know our test is working.

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We know this function is safe to call from anywhere and it'll give us exactly what we want.

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So let's go then call this video done that was Unit testing.

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Very important stuff.

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We just scratched the surface of it.

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But you now know enough to start testing other type of model code.

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You can't really test controllers with unit tests.

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Very very difficult.

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OK.

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And you don't want to test views but whenever there's pure logic that doesn't require any type of use

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like this here math things like that strings anything that you want to do in the business layer and

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the business logic write unit tests for everything in the smallest of the test the smaller the the tests

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the better the more decoupled your functions are the better.

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You don't want function chaining or functions depending on other functions.

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So really important stuff.

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Watch this video again if you forget any of this stuff.

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But that's it for now.

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Marc price of slopes.

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Come let's go on and forward and finish this at.