Building data-driven web apps with Flask and SQLAlchemy Transcripts
Chapter: Testing web apps
Lecture: Special challenges of the web

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0:00 And you'll see that there are some special challenges
0:02 to testing web applications.
0:05 They often have more dependencies
0:07 and other systems tangled up in their code than most.
0:11 Here is the register_post method.
0:14 This is the method that we roughly wrote
0:16 when we want to have a user come to the site
0:19 and create an account.
0:20 They're going to go to the form
0:22 where there's a get version that shows in the form.
0:23 They're going to fill it out
0:24 and they're going to hit post.
0:26 This code is going to run.
0:27 What if we want test this behavior?
0:30 Or if we want to verify
0:31 that its user can register for our site
0:34 if that account email address is not already taken
0:36 and all the details are filled out.
0:38 Let's say if the email is not even filled in
0:41 then we get the right error message and so on.
0:43 We want to test this code.
0:45 What are some of the challenges here?
0:47 Well, look carefully.
0:49 Over here in RegisterViewModel
0:51 remember it imports Flask inside
0:54 and it goes flask.request.
0:56 So, implicitly it expects request to be there
0:59 and to be setup and to have values
1:01 and not be empty. Things like that.
1:03 Wen we call vm.validate
1:05 we see it as actually going to request.form
1:07 and we then get to pull out things
1:09 like the full name and the email and so on.
1:11 We need that to be correctly populated.
1:14 In this user service
1:16 when we try to create the account
1:18 it's probably going to the database
1:20 just like Validate also would
1:22 when it wanted to verify that the account
1:24 didn't already exist. This is going to go to the database
1:27 and maybe insert some data if that worked.
1:29 It might also do some other kind of check as well here.
1:32 Maybe it does other things
1:33 like maybe it registers the user
1:36 at some other API
1:37 like for example, adding the user to our mailing list
1:40 or sending them an email.
1:42 We don't want that to happen.
1:43 We don't want any of those things to happen.
1:45 We want to test in isolation.
1:47 We don't want to depend on the database.
1:49 We don't some random user to get an email
1:52 every time we run this automated test.
1:54 Things like that.
1:55 We want to avoid those.
1:57 Here, when we call login
1:58 this is probably working with the response object
2:00 and calling set_cookie.
2:02 Finally, at the end
2:03 we're doing some kind of redirect with Flask.
2:05 What does that need set up to work?
2:07 So, as you can see
2:08 there's a relatively simple function
2:11 has all sorts of tangled interconnections
2:14 with the web framework
2:16 with the database
2:17 and potentially other services
2:18 like email and external APIs.
2:21 How do we test this?
2:23 We'll see that Python and the test frameworks
2:25 have everything that we need to make this work.
2:28 But, it's going to take a little bit of special attention
2:30 and some cool techniques.