1 00:00:05,670 --> 00:00:08,790 Everybody what's going on this is Caleb with Deb's Lopes dot com. 2 00:00:08,800 --> 00:00:13,900 And in this video we're going to be showing an example of unit testing with swift. 3 00:00:13,920 --> 00:00:17,570 Ok now I'm going to show you an example of some code that I've written. 4 00:00:17,680 --> 00:00:23,410 I'm going to show you some tests that I wrote for that code and then I'm going to show you basically 5 00:00:23,650 --> 00:00:31,180 how a logic error could have been introduced in our application and how my unit test would basically 6 00:00:31,180 --> 00:00:35,270 prevent that from becoming a problem or would basically catch that issue. 7 00:00:35,290 --> 00:00:41,740 So I'm going to pull open a playground that I used here and what I've done is I've imported X C test 8 00:00:41,740 --> 00:00:43,010 which has X codes. 9 00:00:43,060 --> 00:00:44,770 Unit testing platform. 10 00:00:45,190 --> 00:00:49,810 And what I've done is I've basically created a simple class called post. 11 00:00:49,870 --> 00:00:53,840 Think of this like an Instagram post or a Facebook post or even like a tweet. 12 00:00:54,070 --> 00:01:00,490 Of course it's a very simple and incomplete example because there's only a time variable and a time 13 00:01:00,550 --> 00:01:02,160 ago variable. 14 00:01:02,170 --> 00:01:08,650 Think of this sort of like the time stamp of when it was posted and that time is belonging to this Inam 15 00:01:09,160 --> 00:01:12,190 which has different units of time. 16 00:01:12,190 --> 00:01:14,750 Seconds minutes hours days week month year. 17 00:01:14,830 --> 00:01:20,980 OK and they're of type string with a raw value of basically the string representation of themselves. 18 00:01:20,980 --> 00:01:27,670 So we have time ago we have time when it's initialized both those values are set. 19 00:01:27,880 --> 00:01:34,870 Then we have a secondary class called time manager and basically the time manager has a function called 20 00:01:34,870 --> 00:01:37,350 display time ago for post. 21 00:01:37,570 --> 00:01:38,320 OK. 22 00:01:38,440 --> 00:01:41,800 And what we're going to do is pass a post into that function. 23 00:01:41,800 --> 00:01:47,860 We're going to basically set a variable or I guess a constant called time ago and we poll the time ago 24 00:01:47,860 --> 00:01:49,720 value from our post. 25 00:01:49,840 --> 00:01:54,950 We have a pending message of s ago you'll see why that makes sense in just a second. 26 00:01:55,180 --> 00:01:59,500 And then what we do is we return the time ago. 27 00:01:59,650 --> 00:02:05,160 OK the display message so string version of time ago because time ago of course is. 28 00:02:05,180 --> 00:02:09,750 And so if it was you know 24 seconds 24 would be the value here. 29 00:02:09,910 --> 00:02:17,410 Then we add in a space programmatically then we take the time k the raw value of whatever the time is. 30 00:02:17,410 --> 00:02:21,070 So if it was seconds this would be the word second. 31 00:02:21,310 --> 00:02:28,840 And then we add the pending message s ago when it prints out we get 24 seconds ago that's where the 32 00:02:29,260 --> 00:02:30,740 space go comes in. 33 00:02:30,810 --> 00:02:32,280 It depends to the end. 34 00:02:32,290 --> 00:02:41,590 Now we have created an instance of post we've passed in 24 the time a unit is seconds so 24 seconds 35 00:02:41,650 --> 00:02:49,990 ago and the time manager is instantiated and then we call time manager dot display time ago for post 36 00:02:50,380 --> 00:02:55,870 and we print the returning value because of course this creates a string when it returns. 37 00:02:55,870 --> 00:02:57,810 Now this is our implementation code. 38 00:02:57,820 --> 00:03:02,290 Think of you know if you had it in a project or something and now I'm going to show you what it looks 39 00:03:02,290 --> 00:03:06,810 like when we actually create unit tests it'll be inside of an X code project. 40 00:03:06,820 --> 00:03:07,940 But the code is the same. 41 00:03:07,940 --> 00:03:16,060 So I've created a separate class called time manager tests and these tests are basically going to be 42 00:03:16,660 --> 00:03:22,300 for our time manager We're going to test all of the methods and whatever in our time manager class. 43 00:03:22,420 --> 00:03:28,360 Now it is going to inherit from X-C test case that is going to be a must every time. 44 00:03:28,360 --> 00:03:34,270 And basically what we're going to do is we're going to utilize a function called set up and a function 45 00:03:34,270 --> 00:03:35,490 called tear down. 46 00:03:35,590 --> 00:03:39,050 We're actually overriding them from the test case. 47 00:03:39,640 --> 00:03:46,210 But what happens is whenever our tests are run every time a test is run set up is called. 48 00:03:46,210 --> 00:03:52,060 And at the end of the test tear down is called now a set up is good for basically creating instances 49 00:03:52,060 --> 00:03:58,270 of things that we're going to need that we want available at a larger scope. 50 00:03:58,270 --> 00:04:02,440 OK so time manager we want available throughout all of our tests for a time manager. 51 00:04:02,440 --> 00:04:07,080 So we create a variable here and we set its value in set up. 52 00:04:07,210 --> 00:04:11,800 Then when we tear it down we're going to go ahead and set time manager to be equal to nil. 53 00:04:11,800 --> 00:04:15,630 We're basically just going to you know instantiate it and then DISTANCIA it. 54 00:04:15,640 --> 00:04:17,940 That's not a word but you know what I mean. 55 00:04:17,980 --> 00:04:21,480 After the test runs we have a fresh instance every single time. 56 00:04:21,490 --> 00:04:26,620 Now our test here is declared with a function and the beginning of the function is test. 57 00:04:26,620 --> 00:04:30,550 That's how X code knows that it is a test and not another type of function. 58 00:04:30,550 --> 00:04:33,200 So test time display. 59 00:04:33,340 --> 00:04:37,420 I like to write the word or are I guess what we're testing directly after test. 60 00:04:37,420 --> 00:04:43,600 So we're testing the time display and then at the end I put a little underscore and then I say what 61 00:04:43,600 --> 00:04:48,670 the expected result should be it should return a pending message for time. 62 00:04:48,670 --> 00:04:49,390 OK. 63 00:04:49,960 --> 00:04:54,530 And then inside of this test what I've done is I've created a separate instance of post. 64 00:04:54,820 --> 00:04:57,640 I have basically said 58 minutes. 65 00:04:57,760 --> 00:05:04,060 That's what I've passed in then we have created another constant called time ago message that basically 66 00:05:04,060 --> 00:05:10,810 uses our manager that's instantiated upon set up then we call display time ago for post and we pass 67 00:05:10,810 --> 00:05:16,570 in our post the message that gets returned should say 58 minutes ago. 68 00:05:16,720 --> 00:05:20,260 And that's where we use what is called ex-city assert. 69 00:05:20,260 --> 00:05:24,900 There are lots of different kinds of ex-city assert now not just equal. 70 00:05:24,910 --> 00:05:27,990 But there's also LCT assert not nil. 71 00:05:28,060 --> 00:05:32,430 And that verifies that something is not nale as it as you might expect. 72 00:05:32,860 --> 00:05:36,620 There is a certain bill which says yes that is nil. 73 00:05:36,640 --> 00:05:42,130 And you know we could test you know if a value has been properly cleared out or if a property is coming 74 00:05:42,160 --> 00:05:52,240 in as nil or if it is not nil I mean now there is a assert true or false except assert no throw except 75 00:05:52,330 --> 00:05:52,660 assert. 76 00:05:52,660 --> 00:05:57,490 Less then greater then there are a lot of different assertions we can make and basically what we're 77 00:05:57,550 --> 00:06:02,150 saying is we are asserting that a certain thing is true. 78 00:06:02,350 --> 00:06:05,710 OK so if something is false we can assert that it is false. 79 00:06:05,710 --> 00:06:10,480 But what I'm doing is I'm asserting to make sure that this message comes back saying. 80 00:06:10,480 --> 00:06:12,260 58 minutes ago. 81 00:06:12,490 --> 00:06:17,220 Then at the very bottom I called time manager tests default test suite and I run the test. 82 00:06:17,230 --> 00:06:23,640 Now when I actually run it you'll see that my post here 24 seconds it does successfully print out 24 83 00:06:23,650 --> 00:06:24,550 seconds ago. 84 00:06:24,970 --> 00:06:32,140 And our test suite here says the test started the test took point 0 0 3 seconds and we executed one 85 00:06:32,140 --> 00:06:37,990 test with zero failures zero unexpected in zero point zero three seconds. 86 00:06:37,990 --> 00:06:40,200 So that means our test passed. 87 00:06:40,300 --> 00:06:45,830 It means that the message that came back was equal to what we were expecting to get back. 88 00:06:45,850 --> 00:06:49,350 And that means our test works. 89 00:06:49,350 --> 00:06:50,930 K.R. code is good. 90 00:06:50,980 --> 00:06:55,710 Now this is where I'm going to introduce a problem into our application. 91 00:06:55,720 --> 00:06:56,820 OK. 92 00:06:57,070 --> 00:07:02,320 The thing that we're going to do is to show maybe if a junior developer came in and they wanted to change 93 00:07:02,320 --> 00:07:09,040 the code K they wanted to modify it and maybe they thought just you know incorrectly that this already 94 00:07:09,040 --> 00:07:12,160 had all of the values at the end. 95 00:07:12,160 --> 00:07:14,210 I'm going to undo that because it doesn't. 96 00:07:14,350 --> 00:07:19,180 But let's say they thought you know 24 seconds ago they thought Oh it already has the s. 97 00:07:19,240 --> 00:07:22,820 So I'm going to go ahead and this shouldn't be here let's get rid of that code. 98 00:07:22,870 --> 00:07:25,500 So it just says a go at the end. 99 00:07:25,600 --> 00:07:28,600 And of course you can see what printout is wrong. 100 00:07:28,780 --> 00:07:32,130 But look test suite started the test begins. 101 00:07:32,140 --> 00:07:35,080 And look at this example playground error. 102 00:07:35,210 --> 00:07:42,730 Test time display should return a pending message for time ex-city assert equal failed 58 minute ago 103 00:07:43,000 --> 00:07:47,060 is not equal to 58 minutes ago it was working. 104 00:07:47,140 --> 00:07:50,440 Our test passed but now our test fails. 105 00:07:50,440 --> 00:07:54,360 So that means hey there's something wrong in our code something that did work. 106 00:07:54,370 --> 00:07:56,560 At one point now fails. 107 00:07:56,680 --> 00:08:02,830 And so I can look at this error message and say hey 58 minute ago is not equal to 58 minutes ago and 108 00:08:02,830 --> 00:08:09,100 I can go back up here and I can say OK so this function that's supposed to be you know creating the 109 00:08:09,100 --> 00:08:10,370 proper message here. 110 00:08:10,390 --> 00:08:17,410 Oh the appending message is missing s space and now I can run the test again and you'll see all tests 111 00:08:17,410 --> 00:08:18,070 pass. 112 00:08:18,070 --> 00:08:20,830 The code is good so that caught that problem. 113 00:08:20,860 --> 00:08:27,580 If I were to build and run my app the thing that's tricky is that this will still run right just because 114 00:08:27,580 --> 00:08:30,370 the tests fail doesn't mean my project won't run. 115 00:08:30,370 --> 00:08:35,530 If I were to print this out maybe on Instagram below my post if I posted it 24 seconds ago it would 116 00:08:35,530 --> 00:08:41,290 look super unprofessional if it said 24 seconds ago with no space. 117 00:08:41,470 --> 00:08:45,630 So while it will still run it will still successfully compile. 118 00:08:45,700 --> 00:08:50,730 This could accidentally get pushed all the way to production without anybody noticing. 119 00:08:50,890 --> 00:08:55,750 If there weren't unit tests which is why unit testing is so so powerful. 120 00:08:55,750 --> 00:09:02,350 This is a very simple trivial example but there are plenty of instances where things like this could 121 00:09:02,350 --> 00:09:09,430 happen where you could introduce something that technically works but is very very not what you want 122 00:09:09,430 --> 00:09:09,740 to do. 123 00:09:09,760 --> 00:09:16,090 Like this displaying unprofessional text but imagine it was something as simple as this or imagine something 124 00:09:16,090 --> 00:09:23,080 as complex as authentication problems or you know persisting user data things that are a very very big 125 00:09:23,110 --> 00:09:25,290 impact on user experience. 126 00:09:25,300 --> 00:09:30,910 Imagine if those you know successfully passed the code works looks good but you broke something that 127 00:09:30,910 --> 00:09:34,270 did work in the past so that's why unit testing is super powerful. 128 00:09:34,300 --> 00:09:39,940 It helps us to prevent really stupid errors in the future by basically creating a backup of all the 129 00:09:39,940 --> 00:09:45,310 code that works in the past with all the tests that pass so that in the future when things are implemented 130 00:09:45,640 --> 00:09:50,140 we make sure all the tests still pass and make sure that everything still works the way that it's supposed 131 00:09:50,140 --> 00:09:50,290 to. 132 00:09:50,290 --> 00:09:53,580 So unit testing is amazing and super super helpful. 133 00:09:53,590 --> 00:09:55,680 I'm really excited to teach you more about it. 134 00:09:55,690 --> 00:09:57,990 So let's go ahead and let's fix our code here. 135 00:09:58,150 --> 00:10:01,930 Make our test pass and let's head over to the next video. 136 00:10:01,930 --> 00:10:03,900 This is Caleb with Dev slopes dot.com.