Used assertRaisesMessage() to test Django's error messages.

tests/model_forms/tests.py

@@ -180,7 +180,7 @@ class ModelFormBaseTest(TestCase):
     def test_no_model_class(self):
         class NoModelModelForm(forms.ModelForm):
             pass
-        with self.assertRaises(ValueError):
+        with self.assertRaisesMessage(ValueError, 'ModelForm has no model class specified.'):
             NoModelModelForm()
 
     def test_empty_fields_to_fields_for_model(self):
@@ -326,7 +326,7 @@ class ModelFormBaseTest(TestCase):
                 fields = ('name', 'age')
 
     def test_extra_field_modelform_factory(self):
-        with self.assertRaises(FieldError):
+        with self.assertRaisesMessage(FieldError, 'Unknown field(s) (no-field) specified for Person'):
             modelform_factory(Person, fields=['no-field', 'name'])
 
     def test_replace_field(self):
@@ -426,7 +426,8 @@ class ModelFormBaseTest(TestCase):
         form = PriceFormWithoutQuantity({'price': '6.00'})
         self.assertTrue(form.is_valid())
         price = form.save(commit=False)
-        with self.assertRaises(ValidationError):
+        msg = "{'quantity': ['This field cannot be null.']}"
+        with self.assertRaisesMessage(ValidationError, msg):
             price.full_clean()
 
         # The form should not validate fields that it doesn't contain even if they are
@@ -498,11 +499,12 @@ class ModelFormBaseTest(TestCase):
                 pass  # no model
 
         # Can't create new form
-        with self.assertRaises(ValueError):
+        msg = 'ModelForm has no model class specified.'
+        with self.assertRaisesMessage(ValueError, msg):
             InvalidModelForm()
 
         # Even if you provide a model instance
-        with self.assertRaises(ValueError):
+        with self.assertRaisesMessage(ValueError, msg):
             InvalidModelForm(instance=Category)
 
     def test_subcategory_form(self):
@@ -1301,10 +1303,11 @@ class ModelFormBasicTests(TestCase):
             ["Enter a valid 'slug' consisting of letters, numbers, underscores or hyphens."]
         )
         self.assertEqual(f.cleaned_data, {'url': 'foo'})
-        with self.assertRaises(ValueError):
+        msg = "The Category could not be created because the data didn't validate."
+        with self.assertRaisesMessage(ValueError, msg):
             f.save()
         f = BaseCategoryForm({'name': '', 'slug': '', 'url': 'foo'})
-        with self.assertRaises(ValueError):
+        with self.assertRaisesMessage(ValueError, msg):
             f.save()
 
     def test_multi_fields(self):
@@ -1597,7 +1600,8 @@ class ModelChoiceFieldTests(TestCase):
         # instantiated. This proves clean() checks the database during clean() rather
         # than caching it at time of instantiation.
         Category.objects.get(url='4th').delete()
-        with self.assertRaises(ValidationError):
+        msg = "['Select a valid choice. That choice is not one of the available choices.']"
+        with self.assertRaisesMessage(ValidationError, msg):
             f.clean(c4.id)
 
     def test_modelchoicefield_choices(self):
@@ -3045,7 +3049,11 @@ class LocalizedModelFormTest(TestCase):
         self.assertTrue(f.fields['right'].localize)
 
     def test_model_form_refuses_arbitrary_string(self):
-        with self.assertRaises(TypeError):
+        msg = (
+            "BrokenLocalizedTripleForm.Meta.localized_fields "
+            "cannot be a string. Did you mean to type: ('foo',)?"
+        )
+        with self.assertRaisesMessage(TypeError, msg):
             class BrokenLocalizedTripleForm(forms.ModelForm):
                 class Meta:
                     model = Triple