Challenge: Writing Testable Code

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