new form model in apps.dashboard.forms to handle existing item-lists; new test model in .tests.test_forms to accommodate; also new method in .test_views, but skipped for now

src/apps/dashboard/forms.py

@@ -1,6 +1,8 @@
 from django import forms
+from django.core.exceptions import ValidationError
 from .models import Item
 
+DUPLICATE_ITEM_ERROR = "You've already logged this to your list"
 EMPTY_ITEM_ERROR = "You can't have an empty list item"
 
 class ItemForm(forms.models.ModelForm):
@@ -20,3 +22,14 @@ class ItemForm(forms.models.ModelForm):
     def save(self, for_list):
         self.instance.list = for_list
         return super().save()
+
+class ExistingListItemForm(ItemForm):
+    def __init__(self, for_list, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.instance.list = for_list
+
+    def clean_text(self):
+        text = self.cleaned_data["text"]
+        if self.instance.list.item_set.filter(text=text).exists():
+            raise forms.ValidationError(DUPLICATE_ITEM_ERROR)
+        return text

src/apps/dashboard/tests/test_forms.py

@@ -1,5 +1,10 @@
 from django.test import TestCase
-from ..forms import EMPTY_ITEM_ERROR, ItemForm
+from ..forms import (
+    DUPLICATE_ITEM_ERROR,
+    EMPTY_ITEM_ERROR,
+    ExistingListItemForm,
+    ItemForm,
+)
 from ..models import Item, List
 
 class ItemFormTest(TestCase):
@@ -25,3 +30,22 @@ class ItemFormTest(TestCase):
         self.assertEqual(new_item, Item.objects.get())
         self.assertEqual(new_item.text, "do re mi")
         self.assertEqual(new_item.list, mylist)
+
+class ExistingListItemFormTest(TestCase):
+    def test_form_renders_item_text_input(self):
+        list_ = List.objects.create()
+        form = ExistingListItemForm(for_list=list_)
+        self.assertIn('placeholder="Enter a to-do item"', form.as_p())
+
+    def test_form_validation_for_blank_items(self):
+        list_ = List.objects.create()
+        form = ExistingListItemForm(for_list=list_, data={"text": ""})
+        self.assertFalse(form.is_valid())
+        self.assertEqual(form.errors["text"], [EMPTY_ITEM_ERROR])
+
+    def test_form_validation_for_duplicate_items(self):
+        list_ = List.objects.create()
+        Item.objects.create(list=list_, text="twins, basil")
+        form = ExistingListItemForm(for_list=list_, data={"text": "twins, basil"})
+        self.assertFalse(form.is_valid())
+        self.assertEqual(form.errors["text"], [DUPLICATE_ITEM_ERROR])

src/apps/dashboard/tests/test_views.py

@@ -1,5 +1,6 @@
 from django.test import TestCase
 from django.utils import html
+from unittest import skip
 from ..forms import EMPTY_ITEM_ERROR
 from ..models import Item, List
 import lxml.html
@@ -117,3 +118,18 @@ class DashViewTest(TestCase):
     def test_for_invalid_input_shows_error_on_page(self):
         response = self.post_invalid_input()
         self.assertContains(response, html.escape(EMPTY_ITEM_ERROR))
+
+    @skip
+    def test_duplicate_item_validation_errors_end_up_on_lists_page(self):
+        list1 = List.objects.create()
+        Item.objects.create(list=list1, text="lorem ipsum")
+
+        response = self.client.post(
+            f"/apps/dashboard/{list1.id}/",
+            data={"text": "lorem ipsum"},
+        )
+
+        expected_error = html.escape("You've already logged this to your list")
+        self.assertContains(response, expected_error)
+        self.assertTemplateUsed(response, "apps/dashboard/list.html")
+        self.assertEqual(Item.objects.all().count(), 1)