Development with Python

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We do that by passing a new template variable in:
lists/views.py (ch10l017).
except ValidationError:
error = "You can't have an empty list item"
return render(request, 'home.html', { "error": error})
Hmm, it looks like that didn’t quite work:
AssertionError: False is not true : Couldn't find 'You can't have an empty list
item' in response
A little print-based debug…
lists/tests/test_views.py.
expected_error = "You can't have an empty list item"
print (response.content.decode())
self. assertContains(response, expected_error)
…will show us the cause: Django has the apostrophe:
[...]
<span class="help-block">You can&#39;t have an
empty list item</span>
We could hack something like this into our test:
expected_error = "You can&#39;t have an empty list item"
But using Django’s helper function is probably a better idea:
lists/tests/test_views.py (ch10l019).
from django.utils.html import escape
[...]
expected_error = escape("You can't have an empty list item")
self.assertContains(response, expected_error)
That passes!
Ran 12 tests in 0.047s
OK
Checking Invalid Input Isn’t Saved to the Database
Before we go further though, did you notice a little logic error we’ve allowed to creep
into our implementation? We’re currently creating an object, even if validation fails:
lists/views.py.
item = Item. objects.create(text=request. POST['item_text'], list=list_)
try:
item.full_clean()
except ValidationError:
[... ]
Let’s add a new unit test to make sure that empty list items don’t get saved:
Surfacing Model Validation Errors in the View | 181