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In this video we're going to take a look at how we can add in a test to make sure that the new root

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handler in the update root handler are both actually publishing events that get started.

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I'm gonna go back to my underscore underscore mocks Nats wrapper file.

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Inside there we've got that fake implementation of the published function.

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So if we really want to make sure that we are somehow publishing an event off to Nats we really are

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going to want to make sure that this function right here truly gets executed.

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If this thing gets called that means that we are 100 percent trying to actually publish an event rather

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than providing this fake implementation this function.

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We're going to instead provide a mock function a mock function is essentially a fake function but it

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allows us to make tests around it or make expectations around it so we can expect that a mock function

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it's executed or that it gets executed with some particular arguments.

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So I'm going to delete our little fake implementation and I will replace that with just not a fan.

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That is how we create a muck.

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This is going to return a new function and assign it to the property of publish.

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That is a function that can be called from anything inside of application.

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And that function internally is going to keep track of whether or not it has been called what arguments

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it's been provided.

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And so on.

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So we can make some expectations around it.

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Now if we try to run our code like this right now none of our task or a lot of our tests are not going

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to actually pass.

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The reason for that is I remember eventually our publisher the base publisher is going to try to call

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this function that's going to provide a callback function that callback back function must be invoked

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for the publisher to think that everything went ok there's not quite enough to just provide this fake

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function because even though it will be invoked it needs to take the callback function that it will

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be provided and call it.

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In other words we need to still do this right here.

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So we need to still do this but we also want to have a mock function to to kind of do both them together

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to have a mock function and have a custom implementation.

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Here's what we're gonna write out we're gonna put in jest not f n and we'll chain on mock implementation

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and then to this we're going to provide a function.

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So this is the actual function that will be invoked when someone tries to run publish when someone tries

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to run publish it's still going to keep track of the fact that this thing was invoked a number of times

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it was invoked what arguments it was provided and that will allow us to run some tests and whatnot but

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we will also be able to execute this function right here taken that callback and invoke it to make sure

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that the base publisher is still happy.

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Now we do still have to write the same kind of function right here so this thing is going to be invoked

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by the based publisher which means it's going to receive a subject that is a string data that is a string

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and a callback function as well.

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That is a type function that doesn't return anything then inside the function body.

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Once again all we're going to do is execute callback.

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Now we see this right now.

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All of our tests should still run the same thing and go back over my test suite.

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Yeah looks like everything is still running as expected but now we can also start to write out some

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assertions and make sure that that published function is actually being invoked.

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Let me show you how back inside of my new test file I'm going to find roots underscore underscore test

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new test.

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Yes I'm going to go down to the very bottom the thing and I'm going to write out a new expectation or

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new test.

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I'll say it publishes an event

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to mark that function as async and then inside of here I want to try to successfully create a new ticket.

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And then after creating the ticket we're going to try to take a look at that fake function the one we

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just put together the mock one we're going to make sure the thing that that thing was actually invoked

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but to actually create a ticket I'm going to go up to the test that we run out just before I'm going

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to copy where we created a title and then made a request to create a ticket with the title and a given

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price and expected to get back responsive to a one I'm going to copy all that and paste it down inside

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my test so then right after we successfully make this request right after that we should be able to

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say that the publish function was called so to do so we're gonna go to the very top of the file and

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we're going to import the fake Nats wrapper.

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Now when I say fake we're actually going to import the real that's wrapper.

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But once again just even inside of our test file is going to redirect that import for us and it's going

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to instead give us the mark we're gonna try to get the real that's wrapper but it's going to give us

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the mock one instead by going to import Nat's wrapper from up one directory up another Nats dash wrapper

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then down inside the tests we just wrote right now let us do a console lug of Nat's wrapper and I want

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you to see something really interesting.

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Let's save this to flip back over now we're gonna see a lot of console logs right here but one of them

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we should see with a really big console log.

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And here it is right here though it's right underneath the pass statement for a new test.

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Yes.

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Here's the console log.

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We just did.

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You'll notice that this is the fake implementation we just put together.

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This is the contents of the fake or the mock and that's wrapper file though it's some plain object that

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has a client property that has an object that has a public function and the published thing is a mock

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function.

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That's what all this stuff is right here.

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But these are a bunch of helpers that we're going to allow us to make sure that this thing was actually

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called was invoked to some certain arguments and so on.

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So now we can actually write out an expectation down here at the very bottom going to put down here

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expect that's rapper not client not publish.

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To have been called.

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That's how we're going to test this thing and make sure that the publish function actually successfully

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gets invoked right after creating a ticket before testing this out.

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Our terminal.

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One other very quick thing to go inside of our Nats wrapper file.

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We created this mock implementation exactly one time the same mock function gets reused for every single

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one of our tests.

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Though usually between each of our tests we want to reset this mock function.

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Remember the mock function internally is going to record how many times it gets called the different

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arguments it is provided and so on.

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We're going to eventually write out some different expectations about those number of calls the arguments

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and so on.

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We want to make sure that between every single test we reset that data that we're not somehow running

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a test and polluting one test with data from another 10.

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Long story short back inside of our test setup.

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Yes file that's why we're doing all of our initial test config.

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We're gonna find out before each statement and inside there we'll write out.

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Just thought clear all box just have to do that one time and that's pretty much it.

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All right.

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Let's save this.

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Go back over to our terminal and we're going to make sure that all of our tests are passing in specific

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the new test suite.

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Right there.

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Yep looks like it's good.

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That means we are successfully calling that Polish function well well before continuing on because that's

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pretty much it.

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I just want to put every similar test inside of our update file as well and make sure that the published

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function gets called so I gonna go to my update test.

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Yes file at the very top I will import Nats rapper from up one directory up another that's wrapper I'm

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then going to go down to the bottom to file I'll add in it abolishes an event

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then instead of here we want to try to successfully edit or update a ticket and then we will make sure

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that the publish function got invoked so we can very easily come back up to the previous test.

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We'll just take some code right here.

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It looks like this one right here was around testing to make sure a ticket was actually updated.

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I can take everything from cookie on down to right after we do the update with the put we've got cookie

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one request second request I'm going to copy all that go down to the bottom to file a stat all in

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and then right after we'll do and expect that's wrapper client.

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Wish to have an alt right.

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Let's say that run these tests as well and make sure that the update is passing.

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And where is it.

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Yep there it is right there.

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Update is passing.

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Let's say we are good to go.

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Okay.

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That's pretty much it well we've got a working test suite now.

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We also have the ability to add in tests around publishing events which is just fantastic.

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So let's take a pause right here in as usual.

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Continue in just a minute.