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/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])