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Challenge: Writing Testable Code

2:00 with Guil Hernandez and Joseph Fraley

In order to test a random space picker, we’ll need to refactor our code a little to capture a testable output.

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Challenge review

The way computerFire is written is not testable; the only tests we can write for it are trivial and uninformative
Refactor the two "computer" functions I’ve written so that they’re more testable
Try to rewrite the set of functions so that we can still generate random locations
You might need to move the code generating random numbers into their own functions in order to isolate the problem

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One of the best things about BDD is that our code is always testable. 0:00

It has to be because we always write our test first. 0:04

But if you end up with code before tests, 0:08

it can be hard to make a meaningful unit test for existing functions. 0:10

That's because some code is not testable. 0:14

The particular nature of JavaScript means that we have 0:17

access to some code and not other. 0:20

To demonstrate this, in the latest project files for 0:22

this challenge I have written a pair functions that handle a computer player. 0:25

To make a computer player we have to give it a programmatic way of 0:29

placing ships without us knowing. 0:32

And guessing locations during their turn. 0:34

So I've named these functions computerPlaceShip and computerFire. 0:37

I want to write tests for these to make sure they work, but 0:41

the problem is that they produce random results. 0:44

And that's the whole point. 0:47

If the results weren't random, 0:48

then playing against the computer would be predictable, and no fun. 0:50

So, if I write a new suite for computerFire and 0:54

playertest.js, what would I expect to result from the function? 0:57

If the random location it chooses has a ship, 1:02

then I should expect that ship to be damaged. 1:04

But if the random location does not have a ship 1:07

then I should expect the ship to not be damaged. 1:09

I can expect that one of those will happen, but that's not very meaningful. 1:13

It wouldn't tell me much about what the function is doing to say, 1:17

expect (ship.damage).to.have.length{1} or expect(ship.damage).to.be.empty. 1:20

So the way computerFire is written is not testable. 1:27

The only tests we can write for it are trivial and uninformative. 1:31

But we know a lot about testing now. 1:35

So by looking at the two computer functions I've written, 1:37

maybe you can find a way to refactor them so that they're more testable. 1:40

Try to rewrite the set of functions so 1:44

that we can still generate random functions. 1:46

Now you might need to move the code generating random numbers 1:49

into their own functions in order to isolate the problem. 1:52

And in the next video, I'll show you my idea for 1:56

getting the code to be more testable. 1:58

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