Greater Expectations

Okay, so let's start on a new line and still keep our first expectation so 0:00 that if anything breaks along the way we'll know why. 0:06 And you can also go ahead and 0:09 remove the simple test expectation we wrote in the previous video. 0:10 Also go ahead and get rid of the comments. 0:15 So now I'll write a new expectation by typing expect titleCase, 0:21 the great mouse detective. 0:27 Now we don't just want the same string back, right? 0:37 We want the function to give us a different string. 0:39 So in our example, the return string should be 0:42 the great mouse detective with correct capitalization. 0:45 So let's start there. 0:49 This time I'll write .to.equal The Great Mouse Detective. 0:51 Notice how each word begins with a capital letter. 1:00 Now if we save our file and 1:03 run this in the console by typing node textUtilities.js. 1:05 We see that we get an assertion error. 1:16 It says, expected the great mouse detective to equal 1:18 The Great Mouse Detective capitalized. 1:22 Of course, because right now our title case function 1:24 just returns the same string we put in. 1:28 So to make this test pass, we basically need to make our whole function work. 1:32 Now that's a little bit too big and it's not very helpful for 1:37 this test to just tell us make it work like it's doing now. 1:40 So we should break this up into smaller expectations that we know how to tackle. 1:44 Usually, when writing tests the most comprehensive expectations should be 1:53 written last, that way the function passes all the simpler tests first. 1:58 So we'll keep this to.equal expectation at the bottom of all tests, so 2:02 that we know when we finished. 2:07 Then right above it we'll write a new test. 2:09 So now we should think about the smallest piece of the problem we know how to solve. 2:19 So what if we passed in just one letter? 2:24 That shouldn't be hard, right?. 2:27 The function would just return the same letter capitalized. 2:29 So our expectation should be something that captures that. 2:32 So we'll say expect lowercase 2:36 a to equal capital A. 2:42 So now when we save the file, go over to the console and run our test again. 2:48 We can see that it doesn't work yet. 2:53 We get the AssertionError expected lower case a to equal capital A. 2:56 Okay, we can definitely do this because it's built into JavaScript. 3:05 So back in the textUtilities file, I can call the toUpperCase method on our title. 3:08 So now if I save and run the test again, 3:20 we see that we passed our new smaller tests. 3:23 And we still failed the final test but for a different reason. 3:27 So now we're seeing the AssertionError, 3:30 expected THE GREAT MOUSE DETECTIVE to equal The Great Mouse Detective. 3:33 So all caps versus the correct capitalization. 3:37 Well, this is good progress. 3:40 But now we're capitalizing too much instead of not enough. 3:42 So now let's add another expectation with a bit more complexity. 3:50 So right below the expectation, the stroke say expect titleCase. 3:54 To.equal. 4:04 And this time let's use a single word title but more than one letter. 4:10 So first, I'll type the title vertigo in all lower case letter, 4:15 then I'll type Vertigo with a capital V. 4:19 Running the tests gives us the same problem as before but 4:26 it helps to keep the problem small and 4:30 comprehensible by confining our expectation to only one word. 4:32 So instead of uppercasing the entire title, 4:37 let's target just the first character in the title. 4:41 This time, when we run the tests we get, 4:49 expected capital V to equal Vertigo, right? 4:52 Because we're only returning the first letter. 4:56 So back in our function, 4:58 let's add the rest of the title in, skipping over the first letter. 5:00 So right after toUpperCase, we'll say + title.substring and we'll pass one. 5:04 So I'll run the test again in the console and great. 5:14 It looks like we passed our Vertigo test. 5:17 So now our final test says, AssertionError expected, 5:20 The great mouse detective to equal The Great Mouse Detective. 5:24 So the first letter capitalized vs the correct title casing. 5:28 So we're getting closer. 5:32 We know how to capitalize the first letter of a string, we know how to 5:34 add strings together, we just need to do this for each word in the title. 5:38 I think we're ready to try making it work. 5:42 We have a pretty thorough understanding of the problem at this point and 5:44 several tests to keep us on track if we misstep. 5:47 Okay so we know what to do with one word. 5:50 If we keep our final test case to mind, we know we need to break the string apart 5:53 into several pieces so that we can do our one word part on each word in the title. 5:57 And the title case function, we can start by splitting the title up at the spaces. 6:03 I'll type of var words = title.split. 6:08 And I'll leave a space inside the quotes. 6:16 So now we have an array of individual words from our title. 6:19 Now before we even get stuck figuring out the middle, I like to write the return 6:23 statement because I already pretty much know what it will look like. 6:27 We know we have to give back a string that's been title cased. 6:31 We know that somewhere in this function we have to put all the words we 6:34 just separated back together so we may as well do that in the return statement. 6:37 So I'll write return, titleCasedWords.join. 6:42 I know I have to join them back together with a space because that's how 6:50 I took them apart. 6:54 So right now I'm going to just guess that'll make an array called 6:56 titleCasedWords, because I know I have to transform 6:59 all the individual words from my words array somehow. 7:03 All right, so now that I have the start and end of my function, 7:07 a lot is already done for me. 7:11 I know I need to make this array titleCasedWords and 7:12 its value will be derived from the words array. 7:16 So I can at least type var 7:21 titleCaseWords = words. 7:25 Now here's the logic part, I need to loop through all the words, 7:30 do my title case logic on them and then store them in titleCaseWords. 7:34 So let's see, do you already know a function that will do something to each 7:40 member of an array and to give me back an array of the same length? 7:43 Yup, that's right, the map function can do that for us. 7:48 In fact we used this for the gather names of function in the first video. 7:51 So back in my titleCasedWords variable I'll add the map function right 7:57 after words. 8:01 Next I'll move all my titleCase logic for one word into the map callback. 8:10 And now I'll get every word title case to my title. 8:19 So in the map callback, I'll pass word and in the return statement, 8:23 I'll change title to word. 8:27 So now when I save my JavaScript file and run the test again in the console, great. 8:34 It looks like everything passes. 8:40 This function isn't quite finished. 8:43 I'll talk more about covering edge cases in the next stage. 8:45 So far, we've made a lot of assumptions about the input for this function. 8:48 For example, we've always started with a completely lowercase string, 8:52 with no punctuation or weird characters. 8:56 But what happens if we get a title that isn't nicely formatted already? 8:59 Like this type, we might need to expand our function to account for these things. 9:03 For now try and imagine a simple expectation for 9:07 the title case function, that would fail. 9:10 Remember titles don't really capitalize the first letter of every word, 9:13 they skip less important words. 9:17 So you can try fixing the title case function to practice your BDD strategy and 9:19 get more comfortable writing expectations with Chai. 9:24 Even if he had been overwhelmed or 9:27 confused about where to start with our title case function, 9:29 BDD helped us break the problem down into smaller and easier pieces. 9:32 As we work towards passing tests we got a better and better function. 9:37 Not only did red green refactor help us write or code but 9:41 now we actually have some simple tests for our function too. 9:45 It might seem strange at first to just think about these tiny examples and 9:49 expectations but the secret is that this is one of the easiest ways to program. 9:53 Once you get used to writing unit tests your code will also be better 9:58 because you'll have thought about it much more carefully. 10:02 You'll even have tests for your functions that you can show other people 10:04 to explain what your code does or get extra help. 10:08 That's pretty cool. 10:11