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- In this section, we are going to see

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how to organize multiple
tests into suites.

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A suite is a collection of tests.

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It helps you organize your thought process

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when you have a large code base.

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The examples we're going to look at

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in this section are example two.

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So here we are, we are in
lesson one, example two.

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I have some JavaScript code
that contains several functions.

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I have a test file, which
organizes tests into suites,

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collections of tests,
and a package.json file

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that just defines some handy
scripts to run the tests.

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If I open this folder in Visual
Studio Code, here we are.

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We have the test file,

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which we'll look at in detail in a moment.

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We have the code, and as you can see here,

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I've got some simple functions

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to add and subtract two
numbers, to multiply and divide,

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and I've exported all of them.

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This is how you export multiple symbols

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in a common JS module.

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You set the module exports
property to be an object.

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In that object, you specify
the names of the functions

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that you want to export.

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So effectively, an
object is being exported

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and that object has an add
function, a subtract function,

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a multiply and divide.

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Okay, so here we go then.

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In our example,

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here's a code that we're going to test.

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We have an add function,
subtract, multiply, divide,

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and we export from this module,

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from the script, we export
all those four functions.

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Fair enough.

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Okay, so in our test file

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we are going to have two different suites.

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A suite as a group of tests.

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You define a suite using
the describe function.

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The describe function creates a suite

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and it takes two parameters.

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The first parameter is
the name of the suite.

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It's just a free format to text in.

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It describes the purpose of
the tests in this first suite

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and the tests in this second suite.

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And the second parameter
to the described function

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is a Lam function or
Lambda or arrow function.

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And in here, you define all the tests

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for additive operations.

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So I'm going to have a
bunch of tests in this suite

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to test the add and subtract functions.

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I've got another suite here which defines

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my multiplicative functions.

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So in this Lambda, I'll implement my tests

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for the multiply and divide operations.

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Let's take a look at that
file, "example.test.js".

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Let's have a look at that.

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So here it is.

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First of all, I need to
import those functions.

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So I'm going to import from
my example.js file, from here.

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Remember, in my example
JS, I exported an object.

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Okay, so bear that in mind.

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What I then import, this
basically is an object

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that contains a property

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called add, subtract,
multiply, and divide, right?

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So that's an object.

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Okay, so here's my first suite.

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In this first suite,

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which has this textual descriptor,

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I have the body of my
suite contains two tests.

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The first test for the add function,

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and the second test for
the subtract function.

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So just one thing that's
worth noting here.

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This is an object that
contains the imported stuff.

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So in that object, I
called form that object,

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I invoke the add function.

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So that is basically
invoking the add function

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that was exported here.

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Okay, so whatever object
name you give it there,

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you would use that as the prefix.

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So I'm calling the add
function to add two numbers.

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My math suggests that
the results should be 30,

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and then I'm gonna call
the subtract function.

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So these are functions, the
add and subtract functions.

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I've put them under this banner.

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That's my suite of additive functions.

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One of the reasons for grouping tests

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into a suite is that you
can run suites separately.

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We'll see that in a moment.

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You could just run all the
functions in this suite

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or you can just run all the
functions in this suite.

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It's a way of collectively
deciding what tests to run.

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In my second suite, so it
has a textual descriptor,

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"multiplicative functions."

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The parameter here is just a function.

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It's just a grouping mechanism,
really, inside that group.

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I've got another two functions to test,

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that the multiply function works,

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and that the divide function also works.

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Okay, so there we go.

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So what's new here is
the described function.

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This creates a suite.

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I've got one suite for
my additive functions,

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and another suite for my
multiplicative functions.

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Okay, so that's fair enough.

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Now, if you want to, of course,
you can run all the tests.

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You can say "yarn test," or
you can just say "npm run test"

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and that will run all the tests,

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in all the suites, in all the
files in the current folder.

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So we'll do that first.

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Got a command window here
opened into example two.

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Okay, so if I just do an npm run test,

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it'll run all the tests.

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So there were four tests altogether,

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two tests in the additive suite

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and two tests in the multiplicative suite.

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And it runs them all, as we shall see.

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Right, so it's detected that file

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and it displays the
name of the first suite,

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"additive functions."

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In that suite, it found
those two functions.

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So remember, what we
see being displayed here

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is the name of the suite,

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and what we see being displayed here,

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the test that passed,
"adds numbers correctly,"

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that's the descriptor for the
first test, and it worked.

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And the descriptor for the second test,

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"subtracts numbers correctly,"

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obviously, that's this function here.

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And it basically executed
all the tests in the file.

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So the tests in the additive
suite all ran correctly

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and they have a green tick there.

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And the tests in the
multiplicative suite also all ran.

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So all together, we had
four tests that succeeded.

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Okay, so that's marvelous.

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But you know, if you
have a large code base,

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you might have hundreds of
tests and dozens of suites,

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and you don't want to run
all the tests every time,

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because it might take too long.

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So if you want to,

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you can just choose to run
tests from a particular suite.

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And that's the purpose of suites.

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You can choose which tests to run

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instead of running the whole thing.

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So if you want to run just
one suite, you can do this.

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You can say "yarn test"

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and the -t option followed by
a partial suite descriptor.

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This is part of the
name of my first suite.

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Okay, so I could run that
command, yarn test -t.

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And it looks for any
suites that have a name

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that partially matches that.

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And it'll run the tests in that suite.

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You can do the same using npm

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and you have to be a bit more careful.

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When you say npm run, to run the tests,

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you have to have a double dash.

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The double dash syntax, when using npm,

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it indicates that these
parameters here, -t additive,

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these parameters are destined
for the test command.

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Okay? If you didn't put the --

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then these parameters would
be passed into npm run.

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But the -- is like a separator.

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It says, no, no, these parameters

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aren't part of an npm thing.

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These parameters are
part of the test command,

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so that these parameters
will be passed into the test.

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And the test will just
run the additive suite.

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So I'm gonna do that now.

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So npm run, I'm gonna run the test script

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as defined in the
package.json file, remember?

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And then, parameters
into the test command.

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I'm going to pass the -t option

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to say which tests I want to run.

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All tests in any suite
that partially matches

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this name, "additive."

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Okay, so let's see what that displays.

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Quite exciting, isn't it?

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So it detected my test file.

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It realized that this suite
matched that partial name.

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So it ran the tests in that suite.

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Notice, it also detected the other suite,

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but it skipped those tests

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because we told it just
to run the additive tests.

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Okay, so define the tests,
grouping tests in suites,

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it helps you organizationally

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but it also helps you when
you're running the tests.

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You can choose which tests to run

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so that you can get your
work done more quickly.