wip on working incrementally

Author: hjwp

chapter_working_incrementally.asciidoc

@@ -2,18 +2,21 @@
 Working Incrementally
 ---------------------
 
-((("Test-Driven Development (TDD)", "adapting existing code incrementally", id="TDDadapt07")))((("Testing Goat", "working state to working state")))Now
-let's address our real problem, which is that our design only allows for
+((("Test-Driven Development (TDD)", "adapting existing code incrementally", id="TDDadapt07")))
+((("Testing Goat", "working state to working state")))
+Now let's address our real problem, which is that our design only allows for
 one global list.  In this chapter I'll demonstrate a critical TDD technique:
 how to adapt existing code using an incremental, step-by-step process which
 takes you from working state to working state. Testing Goat, not Refactoring
 Cat.
 
+
 Small Design When Necessary
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-((("small vs. big design", id="small07")))((("multiple lists testing", "small vs. big design", id="MLTsmall07")))Let's
-have a think about how we want support for multiple lists to
+((("small vs. big design", id="small07")))
+((("multiple lists testing", "small vs. big design", id="MLTsmall07")))
+Let's have a think about how we want support for multiple lists to
 work.  Currently the FT (which is the closest we have to a design document)
 says this:
 
@@ -38,23 +41,23 @@ don't see each other's lists, and each get their own URL as a way of
 going back to their saved lists.  What might a new design look like?
 
 
+
 Not Big Design Up Front
 ^^^^^^^^^^^^^^^^^^^^^^^
 
-
-
-((("agile movement")))((("Big Design Up Front")))TDD
-is closely associated with the agile movement in software development,
+((("agile movement")))
+((("Big Design Up Front")))
+((("minimum viable applications")))
+TDD is closely associated with the agile movement in software development,
 which includes a reaction against 'Big Design Up Front', the
 traditional software engineering practice whereby, after a lengthy requirements
 gathering exercise, there is an equally lengthy design stage where the
 software is planned out on paper. The agile philosophy is that you learn more
 from solving problems in practice than in theory, especially when you confront
-your application with real users as soon as possible. ((("minimum viable applications")))Instead
-of a long
-up-front design phase, we try to put a 'minimum viable application' out
-there early, and let the design evolve gradually based on feedback from
-real-world usage.
+your application with real users as soon as possible.
+Instead of a long up-front design phase, we try to put a 'minimum viable
+application' out there early, and let the design evolve gradually based on
+feedback from real-world usage.
 
 
 But that doesn't mean that thinking about design is outright banned! In the
@@ -80,8 +83,9 @@ YAGNI!
 ^^^^^^
 
 
-((("Test-Driven Development (TDD)", "philosophy of", "YAGNI")))((("YAGNI (You ain’t gonna need it!)")))Once
-you start thinking about design, it can be hard to stop. All sorts of
+((("Test-Driven Development (TDD)", "philosophy of", "YAGNI")))
+((("YAGNI (You ain’t gonna need it!)")))
+Once you start thinking about design, it can be hard to stop. All sorts of
 other thoughts are occurring to us--we might want to give each list
 a name or title, we might want to recognise users using usernames and
 passwords, we might want to add a longer notes field as well as short
@@ -99,8 +103,9 @@ resist our overenthusiastic creative urges.
 REST (ish)
 ^^^^^^^^^^
 
-((("Representational State Transfer (REST)", "inspiration gained from")))((("Model-View-Controller (MVC) pattern")))We
-have an idea of the data structure we want--the Model part of
+((("Representational State Transfer (REST)", "inspiration gained from")))
+((("Model-View-Controller (MVC) pattern")))
+We have an idea of the data structure we want--the Model part of
 Model-View-Controller (MVC).  What about the View and Controller parts?
 How should the user interact with ++List++s and their ++Item++s using a web browser?
 
@@ -142,8 +147,9 @@ we can send POST requests:
 use a PUT request here--we're just using REST for inspiration. Apart from
 anything else, you can't use PUT in a standard HTML form.)
 
-((("", startref="small07")))((("", startref="MLTsmall07")))In
-summary, our scratchpad for this chapter looks something like this:
+((("", startref="small07")))
+((("", startref="MLTsmall07")))
+In summary, our scratchpad for this chapter looks something like this:
 
 [role="scratchpad"]
 *****
@@ -159,8 +165,9 @@ Implementing the New Design Incrementally Using TDD
 
 
 
-((("Test-Driven Development (TDD)", "overall process of")))((("multiple lists testing", "incremental design implementation")))How
-do we use TDD to implement the new design? Let's take another look at
+((("Test-Driven Development (TDD)", "overall process of")))
+((("multiple lists testing", "incremental design implementation")))
+How do we use TDD to implement the new design? Let's take another look at
 the flowchart for the TDD process in <<TDD-double-loop>>.
 
 At the top level, we're going to use a combination of adding new functionality
@@ -184,8 +191,9 @@ image::images/twp2_0701.png["A flowchart showing functional tests as the overall
 Ensuring We Have a Regression Test
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-((("regression", id="regression07")))((("multiple lists testing", "regression test", id="MLTregression07")))Let's
-translate our scratchpad into a new functional test method, which
+((("regression", id="regression07")))
+((("multiple lists testing", "regression test", id="MLTregression07")))
+Let's translate our scratchpad into a new functional test method, which
 introduces a second user and checks that their to-do list is separate from
 Edith's.
 
@@ -211,7 +219,7 @@ def test_can_start_a_list_for_one_user(self):
 def test_multiple_users_can_start_lists_at_different_urls(self):
     # Edith starts a new to-do list
     self.browser.get(self.live_server_url)
-    inputbox = self.browser.find_element_by_id('id_new_item')
+    inputbox = self.browser.find_element(By.ID, 'id_new_item')
     inputbox.send_keys('Buy peacock feathers')
     inputbox.send_keys(Keys.ENTER)
     self.wait_for_row_in_list_table('1: Buy peacock feathers')
@@ -251,13 +259,13 @@ unique URL for their list:
     # Francis visits the home page.  There is no sign of Edith's
     # list
     self.browser.get(self.live_server_url)
-    page_text = self.browser.find_element_by_tag_name('body').text
+    page_text = self.browser.find_element(By.TAG_NAME, 'body').text
     self.assertNotIn('Buy peacock feathers', page_text)
     self.assertNotIn('make a fly', page_text)
 
     # Francis starts a new list by entering a new item. He
     # is less interesting than Edith...
-    inputbox = self.browser.find_element_by_id('id_new_item')
+    inputbox = self.browser.find_element(By.ID, 'id_new_item')
     inputbox.send_keys('Buy milk')
     inputbox.send_keys(Keys.ENTER)
     self.wait_for_row_in_list_table('1: Buy milk')
@@ -268,7 +276,7 @@ unique URL for their list:
     self.assertNotEqual(francis_list_url, edith_list_url)
 
     # Again, there is no trace of Edith's list
-    page_text = self.browser.find_element_by_tag_name('body').text
+    page_text = self.browser.find_element(By.TAG_NAME, 'body').text
     self.assertNotIn('Buy peacock feathers', page_text)
     self.assertIn('Buy milk', page_text)
 
@@ -295,11 +303,12 @@ $ pass:quotes[*python manage.py test functional_tests*]
 [...]
 .F
 ======================================================================
-FAIL: test_multiple_users_can_start_lists_at_different_urls
-(functional_tests.tests.NewVisitorTest)
+FAIL: test_multiple_users_can_start_lists_at_different_urls (functional_tests.t
+ests.NewVisitorTest.test_multiple_users_can_start_lists_at_different_urls)
+
  ---------------------------------------------------------------------
 Traceback (most recent call last):
-  File "...python-tdd-book/functional_tests/tests.py", line 83, in
+  File "...python-tdd-book/functional_tests/tests.py", line 84, in
 test_multiple_users_can_start_lists_at_different_urls
     self.assertRegex(edith_list_url, '/lists/.+')
 AssertionError: Regex didn't match: '/lists/.+' not found in
@@ -399,15 +408,15 @@ the list table; it's because the URL
 [keep-together]#'/the-only-list-in-the-world/'# doesn't exist yet!
 
 ----
-  File "...python-tdd-book/functional_tests/tests.py", line 57, in
+  File "...python-tdd-book/functional_tests/tests.py", line 58, in
 test_can_start_a_list_for_one_user
 [...]
 selenium.common.exceptions.NoSuchElementException: Message: Unable to locate
 element: [id="id_list_table"]
 
 [...]
 
-  File "...python-tdd-book/functional_tests/tests.py", line 79, in
+  File "...python-tdd-book/functional_tests/tests.py", line 80, in
 test_multiple_users_can_start_lists_at_different_urls
     self.wait_for_row_in_list_table('1: Buy peacock feathers')
 [...]
@@ -479,7 +488,7 @@ TIP: ((("troubleshooting", "URL mappings")))Watch
 out for trailing slashes in URLs, both here in the tests and in
     'urls.py'. They're a common source of bugs.
 
-//TODO: add or link to an explantion about leading and trailing slashes in
+//TODO: add or link to an explanation about leading and trailing slashes in
 //urlpatterns, redirects, etc.
 
 
@@ -489,8 +498,8 @@ out for trailing slashes in URLs, both here in the tests and in
 [source,python]
 ----
 urlpatterns = [
-    url(r'^$', views.home_page, name='home'),
-    url(r'^lists/the-only-list-in-the-world/$', views.view_list, name='view_list'),
+    path('', views.home_page, name='home'),
+    path('lists/the-only-list-in-the-world/', views.view_list, name='view_list'),
 ]
 ----
 ====
@@ -500,15 +509,20 @@ urlpatterns = [
 Running the tests again, we get:
 
 ----
+[...]
+AttributeError: module 'lists.views' has no attribute 'view_list'
+  File "...python-tdd-book/superlists/urls.py", line 6, in <module>
+    path('lists/the-only-list-in-the-world/', views.view_list,
+name='view_list'),
+                                              ^^^^^^^^^^^^^^^
 AttributeError: module 'lists.views' has no attribute 'view_list'
 ----
 
 
+
 A New View Function
 ^^^^^^^^^^^^^^^^^^^
 
-
-
 Nicely self-explanatory.  Let's create a dummy view function in
 'lists/views.py':
 
@@ -559,13 +573,14 @@ Now let's try the FTs again and see what they tell us:
 ----
 FAIL: test_can_start_a_list_for_one_user
 [...]
-  File "...python-tdd-book/functional_tests/tests.py", line 67, in
+  File "...python-tdd-book/functional_tests/tests.py", line 68, in
 test_can_start_a_list_for_one_user
 [...]
 AssertionError: '2: Use peacock feathers to make a fly' not found in ['1: Buy
 peacock feathers']
 
-FAIL: test_multiple_users_can_start_lists_at_different_urls
+FAIL: test_multiple_users_can_start_lists_at_different_urls (functional_tests.t
+ests.NewVisitorTest.test_multiple_users_can_start_lists_at_different_urls)
 [...]
 AssertionError: 'Buy peacock feathers' unexpectedly found in 'Your To-Do
 list\n1: Buy peacock feathers'
@@ -625,7 +640,8 @@ Try that, and we'll see our FTs get back to a happier place:
 
 [subs="specialcharacters,macros"]
 ----
-FAIL: test_multiple_users_can_start_lists_at_different_urls
+FAIL: test_multiple_users_can_start_lists_at_different_urls (functional_tests.t
+ests.NewVisitorTest.test_multiple_users_can_start_lists_at_different_urls)
 [...]
 AssertionError: 'Buy peacock feathers' unexpectedly found in 'Your To-Do
 list\n1: Buy peacock feathers'
@@ -953,9 +969,9 @@ Let's build our new URL now:
 [source,python]
 ----
 urlpatterns = [
-    url(r'^$', views.home_page, name='home'),
-    url(r'^lists/new$', views.new_list, name='new_list'),
-    url(r'^lists/the-only-list-in-the-world/$', views.view_list, name='view_list'),
+    path('', views.home_page, name='home'),
+    path('lists/new', views.new_list, name='new_list'),
+    path('lists/the-only-list-in-the-world/', views.view_list, name='view_list'),
 ]
 ----
 ====
@@ -1080,11 +1096,12 @@ test_can_start_a_list_for_one_user
     self.wait_for_row_in_list_table('1: Buy peacock feathers')
   File "...python-tdd-book/functional_tests/tests.py", line 23, in
 wait_for_row_in_list_table
-    table = self.browser.find_element_by_id('id_list_table')
+    table = self.browser.find_element(By.ID, 'id_list_table')
 selenium.common.exceptions.NoSuchElementException: Message: Unable to locate
 element: [id="id_list_table"]
 
-ERROR: test_multiple_users_can_start_lists_at_different_urls
+FAIL: test_multiple_users_can_start_lists_at_different_urls (functional_tests.t
+ests.NewVisitorTest.test_multiple_users_can_start_lists_at_different_urls)
 [...]
   File "...python-tdd-book/functional_tests/tests.py", line 79, in
 test_multiple_users_can_start_lists_at_different_urls
@@ -1269,12 +1286,10 @@ AttributeError: 'Item' object has no attribute 'list'
 ----
 
 
+
 A Foreign Key Relationship
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-
-
-
 How do we give our `Item` a list attribute?  Let's just try naively making it
 like the `text` attribute (and here's your chance to see whether your
 solution so far looks like mine by the way):
@@ -1337,7 +1352,7 @@ class List(models.Model):
 
 class Item(models.Model):
     text = models.TextField(default='')
-    list = models.ForeignKey(List, default=None)
+    list = models.ForeignKey(List, default=None, on_delete=models.CASCADE)
 ----
 ====
 //030-2
@@ -1579,17 +1594,18 @@ It's time to learn how we can pass parameters from URLs to views:
 [source,python]
 ----
 urlpatterns = [
-    url(r'^$', views.home_page, name='home'),
-    url(r'^lists/new$', views.new_list, name='new_list'),
-    url(r'^lists/(.+)/$', views.view_list, name='view_list'),
+    path('', views.home_page, name='home'),
+    path('lists/new', views.new_list, name='new_list'),
+    path('lists/<list_id>/', views.view_list, name='view_list'),
 ]
 ----
 ====
 //34
 
 
 We adjust the regular expression for our URL to include a 'capture group',
-`(.+)`, which will match any characters, up to the following `/`. The captured
+`<int:list_id>`, which will match any characters, up to the following `/`,
+and try and convert them to being an integer. The captured
 text will get passed to the view as an argument.
 
 In other words, if we go to the URL '/lists/1/', `view_list` will get a second
@@ -1847,15 +1863,15 @@ a little strange. We haven't actually specified a URL for
 getting a 301?
 
 This was a bit of a puzzler! It's because we've used a very "greedy"
-regular expression in our URL:
+capture group in our URL:
 
 
 [role="sourcecode currentcontents"]
 .superlists/urls.py
 ====
 [source,python]
 ----
-    url(r'^lists/(.+)/$', views.view_list, name='view_list'),
+    path('lists/<list_id>/', views.view_list, name='view_list'),
 ----
 ====
 
@@ -1867,14 +1883,14 @@ In this case, [keep-together]#'/lists/1/add_item/'# would be a match for
 guesses that we actually wanted the URL with a trailing slash.
 
 We can fix that by making our URL pattern explicitly capture only numerical
-digits, by using the regular expression `\d`:
+digits, by using the prefix `int:`:
 
 [role="sourcecode"]
 .superlists/urls.py
 ====
 [source,python]
 ----
-    url(r'^lists/(\d+)/$', views.view_list, name='view_list'),
+    path('lists/<int:list_id>/$', views.view_list, name='view_list'),
 ----
 ====
 //38
@@ -2198,13 +2214,12 @@ Then we replace three lines in 'superlists/urls.py' with an `include`:
 ====
 [source,python]
 ----
-from django.conf.urls import include, url
-from lists import views as list_views  #<1>
-from lists import urls as list_urls  #<1>
+from django.urls import path
+from lists import views as list_views
 
 urlpatterns = [
-    url(r'^$', list_views.home_page, name='home'),
-    url(r'^lists/', include(list_urls)),  #<2>
+    path('', views.home_page, name='home'),
+    path('lists/', include('lists.urls')),
 ]
 ----
 ====
@@ -2215,7 +2230,7 @@ urlpatterns = [
     let us import `views` and `urls` from multiple apps if we want--and indeed we
     will need to later on in the book.
 
-<2> Here's the `include`. Notice that it can take a part of a URL regex as a
+<2> Here's the `include`. Notice that it can take a part of a URL as a
     prefix, which will be applied to all the included URLs (this is the bit
     where we reduce duplication, as well as giving our code a better
     structure).