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We're starting to get
the hang of Mocha and BDD and

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we're using it to write
more interesting functions.

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So let's expand our test suite and see
some other things Chai and Mocha can do.

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Now that we can check for a ship,
we also need to register damage on a ship.

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Currently, check for

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ship only reports true or false
depending where ships are located, but

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we need to actually keep track of
the damage each ship has sustained, too.

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So let's start a new test suite to
describe the damage ship function.

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We introduce a test suite and
mocha using describe.

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So right below the check for
ship suite we'll add describe.

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Then we'll pass two arguments,

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the string, damageShip, and a function.

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Then, we'll import the damageShip function
from the ship methods.js file at the top

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of our suite.

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So what do we definitely know about
the way damageShip should work?

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Well, It should probably take a ship,
and a given coordinate of the ship,

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as arguments.

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And we need to know which ship to damage
and which spot to register damage on.

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So, that sounds like a good
expectation of damage ship.

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So we'll create a test spec that
says it should register damage on

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a given ship at a given location.

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So now that we're dealing
with a given ship,

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this function doesn't need any
information about the player object.

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So I'll set up the simplest ship
I need to conduct the test.

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I'll add one ship, one location.

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Then I'll add a damage array to keep
track of the damage that's taken.

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So now I'm going to write
the minimum function I need

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to get the test to run correctly.

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So damaged ship is
different than check for

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ship in that it doesn't return anything.

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So we can't just plug it
into our expect method.

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Instead we have to test the side effects
of damage ship after we call it.

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So inside our spec, if we call,

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damageShip, then past ship and

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the coordinate zero, zero,
what should we expect to be different?

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Well, we should expect the ship's
damage array to be different,

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it should not be empty.

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Remember earlier when we wrote our title
case function, I mentioned that Chai has

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a lot of assertion methods for
making our test easy to write.

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So let's go to the documentation and
see what's available for us to use.

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I've linked to the BDD API docs in
the teacher's notes of this video.

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So, looking through the available methods,
the very first one I see is not.

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And the docs even give me an example.

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So here it says expect
foo to not equal bar.

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Well, that seems useful.

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I've already described my
expectation to myself so

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the damage array should not be empty.

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So I'll just search the page for
empty and see what I get.

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Great, it looks like Chai has
a built in method that checks for

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empty objects, arrays, or strings.

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Cool.

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So this will make it really
easy to write our expectation

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without worrying about how
the real code will work.

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So back inside our spec,
right after damageShip, I'll add

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expect (ship.damage).to.not.be.empty.

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All right, so now, if we save our file and

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run npm test in the console,
we get a type error.

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It says, damageShip is not a function.

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Well, of course because the damage ship
function is missing so let's create it.

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So back inside shipmethod.js,
I'll define the damageShip function.

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And the function will accept
the parameters, ship and coordinates.

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And we'll need to export the function
at the bottom of our file,

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by typing module.exports.damageShip
= damageShip.

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Remember, without these
module.export statements,

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the test files won't have access
to the functions we wrote.

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And they'll fail when we run the tests.

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Alright, so now let's go over
to the console and run npm test.

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So now the test reports a new error,

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it says assertion error,
expected brackets not to be empty.

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So inside the damaged ship function,
we'll say ship.damage.push.

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Then we'll pass coordinates.

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So let's go to the console and
run the test again.

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And great, now the test passes,

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proving that damaged ship can change
the given ship's damage array.

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So now we should add an expectation that
proves we actually added the right thing

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to the array.

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So let's see if Chai can
help us out with this too.

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So once again, I'll search the docs.

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Now I'm not exactly sure what to call
the method I'm looking for here.

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But I do know that I want to check
whether an array has specific members.

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Unfortunately I can't just expect
the first member to equal zero,

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zero because two unique arrays
are never truly equal in JavaScript

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even when they store the same values.

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Every array is a distinct object, but
JavaScript uses strict identity for

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equals, so two arrays could only be equal
if they were really the very same object.

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Not just two objects with all
the same property values.

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We call arrays that look the same
deeply equal, because their deep

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interval values are equal, even though the
arrays themselves are different objects.

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So I'll try searching the page for
array and see what turns up.

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All right, so the first thing I
see is a method called include

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which looks like it checks for an array
for a given value, this is perfect.

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All right, so back inside ship_test.js,
I'll add a new expectation to my spec

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by simply copying this one and
pasting a new one below.

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And this one will say,

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expect(ship.damage).to.include

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zero,zero.

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So now when i go over to the console and

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run the test again,
I see that the test doesn't pass.

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It says expected [ [0,
0 ] ] to include [ 0, 0 ].

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So I can see that the ships.damage
array includes the array I want, but

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Chai doesn't seem to believe it.

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It must be that include doesn't

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really solve our deep
equality problem from before.

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So let's check the docs again.

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Now the problem seems to be deep equality.

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So I'll try searching the page for
deep and see what comes up.

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Great, so this method here
looks good because it allows

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us to make deep equality comparisons,
which is exactly what we need.

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So now I can write an expectation about
the first member of the damage array,

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by changing this expectation here
at the bottom to expect ship.damage

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zero to.deep.equal zero, zero.

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So I'll say to.deep.equal.

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So, basically,

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just check that the first element of
the damage array looks like this.

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All right so now if we save this file and
run npm test in the console.

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Great, it looks like
everything is passing.

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Now we could complicate
the damage ship function by first

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making sure that the ship hasn't already
taken damage at the given location,

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by making sure the location is valid and
so on, but this will do for now.

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Now we need a method that players
can call during the game in order to

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fire on their opponent.

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It should use check for ship to
confirm the attacking player's guess.

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And it should use damage ship to
register damage on their opponent.

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Try and write a test suite for

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this fire function using some of
the assertion methods you learned.

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Like equal, not.equal,
deep.equal, .include and so on.

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You might even check the documentation
to find something more useful for

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your test spec idea.

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The link to that documentation is in
the teacher's notes of this video.

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And if you're feeling confident you
can even try implementing the function

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based on your test suite.

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We've already been using BDD this
whole time, I think you can do it.

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And when you're done, I'll show
you my approach in the next video.