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In this lesson we're going to continue to explore new testing techniques and the goal here is to figure

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out how we can mock our NPM modules so the process of marking is the process of replacing the real functions

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that run with functions that you create when we're running in a test environment.

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Now why might that be something we ever want to do.

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Well let's think about what all of this code actually does.

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We run various endpoints like the one for signing up and the one for deleting accounts.

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And we know that when both of these execute emails are sent behind the scenes emails are sent to email

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addresses that don't exist and will never be checked.

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And that alone might not be the worst thing.

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The problem though is that we're constantly rerunning our test cases which means we're just racking

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up unnecessary emails being sent from our set grid account.

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Now if we're on the free plan that means we don't have many free emails to send.

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And if we're on a paid plan and that means we're wasting money on emails that will never be opened with

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mocking we can make sure that when our program is running using just we don't actually send those emails

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off.

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Well let's get started by creating the directory where we can store our marks.

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So right inside of the test folder if we're trying to mock and NPM module what do we do we create a

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MOX directory.

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Now it starts with two underscores that's two there and not just one.

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Then we type out MOX in lower case than it's two more underscores this is the directory name that just

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is going to look for now in here we can create files for the individual modules we're trying to mock.

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So if I wanted to mock something like Jason Webb token I would create Jason Webb.

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Token dot J S in the MOX directory in this case we're trying to mark the module used right here that

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is at seven grid forward slash male.

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Now right here they are using at followed by the organization then forward slash the individual utility.

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This is known as NPM scope and all that means for us is that we're going to create a directory with

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this name inside of MOX.

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Then in that folder it will create a file with this name and the J.S. extension that will allow us to

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mark out the functionality providing our own versions of set API key and send to use when running in

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test mode.

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So right here let's get that done in the MOX folder will create a new folder at send a grid and in the

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send grid directory it will create a new file this one mail dot J S.

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Now it's important that when we're marking out a module we provide all of the things that that module

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needs in order to work.

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So our application code is expecting things like set API key and send to actually exist.

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So if we're going to mark that module out we need to provide our own versions of all of this.

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So the code at least doesn't fail.

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So right here that means we need to export an object with those properties on it because that's exactly

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what set grid is doing.

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We get an object back with those properties sitting right on it.

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So over here will actually kick things off by using module exports and setting it equal to a new empty

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object.

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And on here we'll provide a set API key and send no down below you'll actually notice that our test

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suite is failing and if we scroll up we can see why right here test suite failed to run.

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And that's referring to our user test suite.

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And the reason is that s g mail dot set API key is not a function.

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And they're right now the reason this is happening is because we've provided a mark for that module

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but we're not exporting an object with that function defined.

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So let's fix it right here on this object.

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I'm going to set a value for set API key.

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I'll go ahead and set it equal to a new function and I'll do the same thing down below for the other

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method we're using sent.

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Now if we were using even other methods from the module we would want to mark those as well.

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Now when it comes to mocking you could choose to accept arguments and then return some sort of fixed

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value.

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In this case in account dot J S we pass in arguments like the email to be sent or the API key to be

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set.

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But we don't do anything with the return value.

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So there's actually no need to do anything inside of these functions.

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All this is gonna do is allow these functions to be called over here but in reality nothing is happening

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behind the scenes and that's good in the test environment.

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No api keys will be set and no emails will get sent now if I go ahead and save male dot J S we'll see

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that our test suite does restart and this time it should be brought back to its working state.

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And it is.

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Now if you want to learn more about MOX as always it's defined in the documentation like everything

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else we have explored related to just under guides in the sidebar.

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There's a page called the manual marks which covers everything we just talked about right here a mocking

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note modules outlines what we just did.

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So that's where we're going to stop for this one.

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I wanted to introduce the concept of marking allowing us to not send those e-mails from our test environment

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though we won't be using them for anything else in this test suite.

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The nice thing now though is that as our test suite reruns we're not going to be wasting our limited

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emails that we can send off.

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All right.

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That's where we're going to stop for this one.

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I'm excited to continue on.

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So I'll see you in the next lesson.