new save FBVs, methods & test methods

src/apps/dashboard/forms.py

@@ -32,4 +32,7 @@ class ExistingListItemForm(ItemForm):
         text = self.cleaned_data["text"]
         if self.instance.list.item_set.filter(text=text).exists():
             raise forms.ValidationError(DUPLICATE_ITEM_ERROR)
-        return text
+        return text
+    
+    def save(self):
+        return forms.models.ModelForm.save(self)