Moved remaining SimpleTestCase.assertFormError()/assertFormsetErrors() tests to test_utils.

This also removes redundant tests in test_client_regress.

Follow up to 68144f40490b2572c8da4341742b9e387e3f6bdd.

4 files changed, 135 insertions, 398 deletions

diff --git a/tests/test_client/urls.py b/tests/test_client/urls.py
index 9ccd219fb5..2508346cf8 100644
--- a/tests/test_client/urls.py
+++ b/tests/test_client/urls.py
@@ -42,7 +42,6 @@ urlpatterns = [
     path("bad_view/", views.bad_view),
     path("form_view/", views.form_view),
     path("form_view_with_template/", views.form_view_with_template),
-    path("formset_view/", views.formset_view),
     path("json_view/", views.json_view),
     path("login_protected_view/", views.login_protected_view),
     path("login_protected_method_view/", views.login_protected_method_view),
diff --git a/tests/test_client/views.py b/tests/test_client/views.py
index 4dc58fab8d..cff0463788 100644
--- a/tests/test_client/views.py
+++ b/tests/test_client/views.py
@@ -7,7 +7,6 @@ from django.core import mail
 from django.core.exceptions import ValidationError
 from django.forms import fields
 from django.forms.forms import Form
-from django.forms.formsets import BaseFormSet, formset_factory
 from django.http import (
     HttpResponse,
     HttpResponseBadRequest,
@@ -259,48 +258,6 @@ def form_view_with_template(request):
     )
 
 
-class BaseTestFormSet(BaseFormSet):
-    def clean(self):
-        """No two email addresses are the same."""
-        if any(self.errors):
-            # Don't bother validating the formset unless each form is valid
-            return
-
-        emails = []
-        for form in self.forms:
-            email = form.cleaned_data["email"]
-            if email in emails:
-                raise ValidationError(
-                    "Forms in a set must have distinct email addresses."
-                )
-            emails.append(email)
-
-
-TestFormSet = formset_factory(TestForm, BaseTestFormSet)
-
-
-def formset_view(request):
-    "A view that tests a simple formset"
-    if request.method == "POST":
-        formset = TestFormSet(request.POST)
-        if formset.is_valid():
-            t = Template("Valid POST data.", name="Valid POST Template")
-            c = Context()
-        else:
-            t = Template(
-                "Invalid POST data. {{ my_formset.errors }}",
-                name="Invalid POST Template",
-            )
-            c = Context({"my_formset": formset})
-    else:
-        formset = TestForm(request.GET)
-        t = Template(
-            "Viewing base formset. {{ my_formset }}.", name="Formset GET Template"
-        )
-        c = Context({"my_formset": formset})
-    return HttpResponse(t.render(c))
-
-
 @login_required
 def login_protected_view(request):
     "A simple view that is login protected."
diff --git a/tests/test_client_regress/tests.py b/tests/test_client_regress/tests.py
index 43cc9580cc..aaf25e2ec4 100644
--- a/tests/test_client_regress/tests.py
+++ b/tests/test_client_regress/tests.py
@@ -616,360 +616,6 @@ class AssertRedirectsTests(SimpleTestCase):
 
 
 @override_settings(ROOT_URLCONF="test_client_regress.urls")
-class AssertFormErrorTests(SimpleTestCase):
-    def test_unknown_form(self):
-        "An assertion is raised if the form name is unknown"
-        post_data = {
-            "text": "Hello World",
-            "email": "not an email address",
-            "value": 37,
-            "single": "b",
-            "multi": ("b", "c", "e"),
-        }
-        response = self.client.post("/form_view/", post_data)
-        self.assertEqual(response.status_code, 200)
-        self.assertTemplateUsed(response, "Invalid POST Template")
-
-        msg = "The form 'wrong_form' was not used to render the response"
-        with self.assertRaisesMessage(AssertionError, msg):
-            self.assertFormError(response, "wrong_form", "some_field", "Some error.")
-        with self.assertRaisesMessage(AssertionError, "abc: " + msg):
-            self.assertFormError(
-                response, "wrong_form", "some_field", "Some error.", msg_prefix="abc"
-            )
-
-    def test_unknown_field(self):
-        "An assertion is raised if the field name is unknown"
-        post_data = {
-            "text": "Hello World",
-            "email": "not an email address",
-            "value": 37,
-            "single": "b",
-            "multi": ("b", "c", "e"),
-        }
-        response = self.client.post("/form_view/", post_data)
-        self.assertEqual(response.status_code, 200)
-        self.assertTemplateUsed(response, "Invalid POST Template")
-
-        msg = (
-            "The form <TestForm bound=True, valid=False, "
-            "fields=(text;email;value;single;multi)> does not contain the field "
-            "'some_field'."
-        )
-        with self.assertRaisesMessage(AssertionError, msg):
-            self.assertFormError(response, "form", "some_field", "Some error.")
-        with self.assertRaisesMessage(AssertionError, "abc: " + msg):
-            self.assertFormError(
-                response, "form", "some_field", "Some error.", msg_prefix="abc"
-            )
-
-    def test_noerror_field(self):
-        "An assertion is raised if the field doesn't have any errors"
-        post_data = {
-            "text": "Hello World",
-            "email": "not an email address",
-            "value": 37,
-            "single": "b",
-            "multi": ("b", "c", "e"),
-        }
-        response = self.client.post("/form_view/", post_data)
-        self.assertEqual(response.status_code, 200)
-        self.assertTemplateUsed(response, "Invalid POST Template")
-
-        msg = (
-            "The errors of field 'value' on form <TestForm bound=True, valid=False, "
-            "fields=(text;email;value;single;multi)> don't match."
-        )
-        with self.assertRaisesMessage(AssertionError, msg):
-            self.assertFormError(response, "form", "value", "Some error.")
-        with self.assertRaisesMessage(AssertionError, "abc: " + msg):
-            self.assertFormError(
-                response, "form", "value", "Some error.", msg_prefix="abc"
-            )
-
-    def test_unknown_error(self):
-        "An assertion is raised if the field doesn't contain the provided error"
-        post_data = {
-            "text": "Hello World",
-            "email": "not an email address",
-            "value": 37,
-            "single": "b",
-            "multi": ("b", "c", "e"),
-        }
-        response = self.client.post("/form_view/", post_data)
-        self.assertEqual(response.status_code, 200)
-        self.assertTemplateUsed(response, "Invalid POST Template")
-
-        msg = (
-            "The errors of field 'email' on form <TestForm bound=True, valid=False, "
-            "fields=(text;email;value;single;multi)> don't match."
-        )
-        with self.assertRaisesMessage(AssertionError, msg):
-            self.assertFormError(response, "form", "email", "Some error.")
-        with self.assertRaisesMessage(AssertionError, "abc: " + msg):
-            self.assertFormError(
-                response, "form", "email", "Some error.", msg_prefix="abc"
-            )
-
-    def test_unknown_nonfield_error(self):
-        """
-        An assertion is raised if the form's non field errors doesn't contain
-        the provided error.
-        """
-        post_data = {
-            "text": "Hello World",
-            "email": "not an email address",
-            "value": 37,
-            "single": "b",
-            "multi": ("b", "c", "e"),
-        }
-        response = self.client.post("/form_view/", post_data)
-        self.assertEqual(response.status_code, 200)
-        self.assertTemplateUsed(response, "Invalid POST Template")
-
-        msg = (
-            "The non-field errors of form <TestForm bound=True, valid=False, "
-            "fields=(text;email;value;single;multi)> don't match."
-        )
-        with self.assertRaisesMessage(AssertionError, msg):
-            self.assertFormError(response, "form", None, "Some error.")
-        with self.assertRaisesMessage(AssertionError, "abc: " + msg):
-            self.assertFormError(
-                response, "form", None, "Some error.", msg_prefix="abc"
-            )
-
-
-@override_settings(ROOT_URLCONF="test_client_regress.urls")
-class AssertFormsetErrorTests(SimpleTestCase):
-    msg_prefixes = [("", {}), ("abc: ", {"msg_prefix": "abc"})]
-
-    def setUp(self):
-        """Makes response object for testing field and non-field errors"""
-        # For testing field and non-field errors
-        self.response_form_errors = self.getResponse(
-            {
-                "form-TOTAL_FORMS": "2",
-                "form-INITIAL_FORMS": "2",
-                "form-0-text": "Raise non-field error",
-                "form-0-email": "not an email address",
-                "form-0-value": 37,
-                "form-0-single": "b",
-                "form-0-multi": ("b", "c", "e"),
-                "form-1-text": "Hello World",
-                "form-1-email": "email@domain.com",
-                "form-1-value": 37,
-                "form-1-single": "b",
-                "form-1-multi": ("b", "c", "e"),
-            }
-        )
-        # For testing non-form errors
-        self.response_nonform_errors = self.getResponse(
-            {
-                "form-TOTAL_FORMS": "2",
-                "form-INITIAL_FORMS": "2",
-                "form-0-text": "Hello World",
-                "form-0-email": "email@domain.com",
-                "form-0-value": 37,
-                "form-0-single": "b",
-                "form-0-multi": ("b", "c", "e"),
-                "form-1-text": "Hello World",
-                "form-1-email": "email@domain.com",
-                "form-1-value": 37,
-                "form-1-single": "b",
-                "form-1-multi": ("b", "c", "e"),
-            }
-        )
-
-    def getResponse(self, post_data):
-        response = self.client.post("/formset_view/", post_data)
-        self.assertEqual(response.status_code, 200)
-        self.assertTemplateUsed(response, "Invalid POST Template")
-        return response
-
-    def test_unknown_formset(self):
-        "An assertion is raised if the formset name is unknown"
-        for prefix, kwargs in self.msg_prefixes:
-            msg = (
-                prefix
-                + "The formset 'wrong_formset' was not used to render the response"
-            )
-            with self.assertRaisesMessage(AssertionError, msg):
-                self.assertFormsetError(
-                    self.response_form_errors,
-                    "wrong_formset",
-                    0,
-                    "Some_field",
-                    "Some error.",
-                    **kwargs,
-                )
-
-    def test_unknown_field(self):
-        "An assertion is raised if the field name is unknown"
-        for prefix, kwargs in self.msg_prefixes:
-            msg = (
-                f"{prefix}The form 0 of formset <TestFormFormSet: bound=True "
-                f"valid=False total_forms=2> does not contain the field 'Some_field'."
-            )
-            with self.assertRaisesMessage(AssertionError, msg):
-                self.assertFormsetError(
-                    self.response_form_errors,
-                    "my_formset",
-                    0,
-                    "Some_field",
-                    "Some error.",
-                    **kwargs,
-                )
-
-    def test_no_error_field(self):
-        "An assertion is raised if the field doesn't have any errors"
-        for prefix, kwargs in self.msg_prefixes:
-            msg = (
-                f"{prefix}The errors of field 'value' on form 1 of formset "
-                f"<TestFormFormSet: bound=True valid=False total_forms=2> don't match."
-            )
-            with self.assertRaisesMessage(AssertionError, msg):
-                self.assertFormsetError(
-                    self.response_form_errors,
-                    "my_formset",
-                    1,
-                    "value",
-                    "Some error.",
-                    **kwargs,
-                )
-
-    def test_unknown_error(self):
-        "An assertion is raised if the field doesn't contain the specified error"
-        for prefix, kwargs in self.msg_prefixes:
-            msg = (
-                f"{prefix}The errors of field 'email' on form 0 of formset "
-                f"<TestFormFormSet: bound=True valid=False total_forms=2> don't match."
-            )
-            with self.assertRaisesMessage(AssertionError, msg):
-                self.assertFormsetError(
-                    self.response_form_errors,
-                    "my_formset",
-                    0,
-                    "email",
-                    "Some error.",
-                    **kwargs,
-                )
-
-    def test_field_error(self):
-        "No assertion is raised if the field contains the provided error"
-        error_msg = ["Enter a valid email address."]
-        for prefix, kwargs in self.msg_prefixes:
-            self.assertFormsetError(
-                self.response_form_errors, "my_formset", 0, "email", error_msg, **kwargs
-            )
-
-    def test_no_nonfield_error(self):
-        """
-        An assertion is raised if the formsets non-field errors doesn't contain
-        any errors.
-        """
-        for prefix, kwargs in self.msg_prefixes:
-            msg = (
-                f"{prefix}The non-field errors of form 1 of formset <TestFormFormSet: "
-                f"bound=True valid=False total_forms=2> don't match."
-            )
-            with self.assertRaisesMessage(AssertionError, msg):
-                self.assertFormsetError(
-                    self.response_form_errors,
-                    "my_formset",
-                    1,
-                    None,
-                    "Some error.",
-                    **kwargs,
-                )
-
-    def test_unknown_nonfield_error(self):
-        """
-        An assertion is raised if the formsets non-field errors doesn't contain
-        the provided error.
-        """
-        for prefix, kwargs in self.msg_prefixes:
-            msg = (
-                f"{prefix}The non-field errors of form 0 of formset <TestFormFormSet: "
-                f"bound=True valid=False total_forms=2> don't match."
-            )
-            with self.assertRaisesMessage(AssertionError, msg):
-                self.assertFormsetError(
-                    self.response_form_errors,
-                    "my_formset",
-                    0,
-                    None,
-                    "Some error.",
-                    **kwargs,
-                )
-
-    def test_nonfield_error(self):
-        """
-        No assertion is raised if the formsets non-field errors contains the
-        provided error.
-        """
-        for prefix, kwargs in self.msg_prefixes:
-            self.assertFormsetError(
-                self.response_form_errors,
-                "my_formset",
-                0,
-                None,
-                "Non-field error.",
-                **kwargs,
-            )
-
-    def test_no_nonform_error(self):
-        """
-        An assertion is raised if the formsets non-form errors doesn't contain
-        any errors.
-        """
-        for prefix, kwargs in self.msg_prefixes:
-            msg = (
-                f"{prefix}The non-form errors of formset <TestFormFormSet: bound=True "
-                f"valid=False total_forms=2> don't match"
-            )
-            with self.assertRaisesMessage(AssertionError, msg):
-                self.assertFormsetError(
-                    self.response_form_errors,
-                    "my_formset",
-                    None,
-                    None,
-                    "Some error.",
-                    **kwargs,
-                )
-
-    def test_unknown_nonform_error(self):
-        """
-        An assertion is raised if the formsets non-form errors doesn't contain
-        the provided error.
-        """
-        for prefix, kwargs in self.msg_prefixes:
-            msg = (
-                f"{prefix}The non-form errors of formset <TestFormFormSet: bound=True "
-                f"valid=False total_forms=2> don't match"
-            )
-            with self.assertRaisesMessage(AssertionError, msg):
-                self.assertFormsetError(
-                    self.response_nonform_errors,
-                    "my_formset",
-                    None,
-                    None,
-                    "Some error.",
-                    **kwargs,
-                )
-
-    def test_nonform_error(self):
-        """
-        No assertion is raised if the formsets non-form errors contains the
-        provided error.
-        """
-        msg = "Forms in a set must have distinct email addresses."
-        for prefix, kwargs in self.msg_prefixes:
-            self.assertFormsetError(
-                self.response_nonform_errors, "my_formset", None, None, msg, **kwargs
-            )
-
-
-@override_settings(ROOT_URLCONF="test_client_regress.urls")
 class LoginTests(TestDataMixin, TestCase):
     def test_login_different_client(self):
         "Using a different test client doesn't violate authentication"
diff --git a/tests/test_utils/tests.py b/tests/test_utils/tests.py
index 2dfcdd6804..e0204e7083 100644
--- a/tests/test_utils/tests.py
+++ b/tests/test_utils/tests.py
@@ -1402,6 +1402,11 @@ class AssertFormErrorTests(SimpleTestCase):
         response = mock.Mock(context=[{}])
         with self.assertRaisesMessage(AssertionError, msg):
             self.assertFormError(response, "form", "field", "invalid value")
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormError(
+                response, "form", "field", "invalid value", msg_prefix=msg_prefix
+            )
 
     def test_field_not_in_form(self):
         msg = (
@@ -1411,6 +1416,11 @@ class AssertFormErrorTests(SimpleTestCase):
         response = mock.Mock(context=[{"form": TestForm.invalid()}])
         with self.assertRaisesMessage(AssertionError, msg):
             self.assertFormError(response, "form", "other_field", "invalid value")
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormError(
+                response, "form", "other_field", "invalid value", msg_prefix=msg_prefix
+            )
 
     def test_field_with_no_errors(self):
         msg = (
@@ -1421,6 +1431,11 @@ class AssertFormErrorTests(SimpleTestCase):
         with self.assertRaisesMessage(AssertionError, msg) as ctx:
             self.assertFormError(response, "form", "field", "invalid value")
         self.assertIn("[] != ['invalid value']", str(ctx.exception))
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormError(
+                response, "form", "field", "invalid value", msg_prefix=msg_prefix
+            )
 
     def test_field_with_different_error(self):
         msg = (
@@ -1431,6 +1446,11 @@ class AssertFormErrorTests(SimpleTestCase):
         with self.assertRaisesMessage(AssertionError, msg) as ctx:
             self.assertFormError(response, "form", "field", "other error")
         self.assertIn("['invalid value'] != ['other error']", str(ctx.exception))
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormError(
+                response, "form", "field", "other error", msg_prefix=msg_prefix
+            )
 
     def test_basic_positive_assertion(self):
         response = mock.Mock(context=[{"form": TestForm.invalid()}])
@@ -1470,6 +1490,23 @@ class AssertFormErrorTests(SimpleTestCase):
         response = mock.Mock(context=[{"form": TestForm.invalid(nonfield=True)}])
         self.assertFormError(response, "form", None, "non-field error")
 
+    def test_different_non_field_errors(self):
+        response = mock.Mock(context=[{"form": TestForm.invalid(nonfield=True)}])
+        msg = (
+            "The non-field errors of form <TestForm bound=True, valid=False, "
+            "fields=(field)> don't match."
+        )
+        with self.assertRaisesMessage(AssertionError, msg) as ctx:
+            self.assertFormError(response, "form", None, "other non-field error")
+        self.assertIn(
+            "['non-field error'] != ['other non-field error']", str(ctx.exception)
+        )
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormError(
+                response, "form", None, "other non-field error", msg_prefix=msg_prefix
+            )
+
     @ignore_warnings(category=RemovedInDjango50Warning)
     def test_errors_none(self):
         msg = (
@@ -1518,6 +1555,11 @@ class AssertFormsetErrorTests(SimpleTestCase):
         response = mock.Mock(context=[{}])
         with self.assertRaisesMessage(AssertionError, msg):
             self.assertFormsetError(response, "formset", 0, "field", "invalid value")
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormsetError(
+                response, "formset", 0, "field", "invalid value", msg_prefix=msg_prefix
+            )
 
     def test_field_not_in_form(self):
         msg = (
@@ -1533,6 +1575,16 @@ class AssertFormsetErrorTests(SimpleTestCase):
                 "other_field",
                 "invalid value",
             )
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormsetError(
+                response,
+                "formset",
+                0,
+                "other_field",
+                "invalid value",
+                msg_prefix=msg_prefix,
+            )
 
     def test_field_with_no_errors(self):
         msg = (
@@ -1543,6 +1595,11 @@ class AssertFormsetErrorTests(SimpleTestCase):
         with self.assertRaisesMessage(AssertionError, msg) as ctx:
             self.assertFormsetError(response, "formset", 0, "field", "invalid value")
         self.assertIn("[] != ['invalid value']", str(ctx.exception))
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormsetError(
+                response, "formset", 0, "field", "invalid value", msg_prefix=msg_prefix
+            )
 
     def test_field_with_different_error(self):
         msg = (
@@ -1553,6 +1610,11 @@ class AssertFormsetErrorTests(SimpleTestCase):
         with self.assertRaisesMessage(AssertionError, msg) as ctx:
             self.assertFormsetError(response, "formset", 0, "field", "other error")
         self.assertIn("['invalid value'] != ['other error']", str(ctx.exception))
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormsetError(
+                response, "formset", 0, "field", "other error", msg_prefix=msg_prefix
+            )
 
     def test_basic_positive_assertion(self):
         response = mock.Mock(context=[{"formset": TestFormset.invalid()}])
@@ -1594,6 +1656,47 @@ class AssertFormsetErrorTests(SimpleTestCase):
         )
         self.assertFormsetError(response, "formset", 0, None, "non-field error")
 
+    def test_different_non_field_errors(self):
+        response = mock.Mock(
+            context=[{}, {"formset": TestFormset.invalid(nonfield=True)}],
+        )
+        msg = (
+            "The non-field errors of form 0 of formset <TestFormset: bound=True "
+            "valid=False total_forms=1> don't match."
+        )
+        with self.assertRaisesMessage(AssertionError, msg) as ctx:
+            self.assertFormsetError(
+                response, "formset", 0, None, "other non-field error"
+            )
+        self.assertIn(
+            "['non-field error'] != ['other non-field error']", str(ctx.exception)
+        )
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormsetError(
+                response,
+                "formset",
+                0,
+                None,
+                "other non-field error",
+                msg_prefix=msg_prefix,
+            )
+
+    def test_no_non_field_errors(self):
+        response = mock.Mock(context=[{}, {"formset": TestFormset.invalid()}])
+        msg = (
+            "The non-field errors of form 0 of formset <TestFormset: bound=True "
+            "valid=False total_forms=1> don't match."
+        )
+        with self.assertRaisesMessage(AssertionError, msg) as ctx:
+            self.assertFormsetError(response, "formset", 0, None, "non-field error")
+        self.assertIn("[] != ['non-field error']", str(ctx.exception))
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormsetError(
+                response, "formset", 0, None, "non-field error", msg_prefix=msg_prefix
+            )
+
     def test_non_form_errors(self):
         response = mock.Mock(
             context=[
@@ -1603,6 +1706,38 @@ class AssertFormsetErrorTests(SimpleTestCase):
         )
         self.assertFormsetError(response, "formset", None, None, "error")
 
+    def test_different_non_form_errors(self):
+        response = mock.Mock(
+            context=[{}, {"formset": TestFormset.invalid(nonform=True)}],
+        )
+        msg = (
+            "The non-form errors of formset <TestFormset: bound=True valid=False "
+            "total_forms=0> don't match."
+        )
+        with self.assertRaisesMessage(AssertionError, msg) as ctx:
+            self.assertFormsetError(response, "formset", None, None, "other error")
+        self.assertIn("['error'] != ['other error']", str(ctx.exception))
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormsetError(
+                response, "formset", None, None, "other error", msg_prefix=msg_prefix
+            )
+
+    def test_no_non_form_errors(self):
+        response = mock.Mock(context=[{}, {"formset": TestFormset.invalid()}])
+        msg = (
+            "The non-form errors of formset <TestFormset: bound=True valid=False "
+            "total_forms=1> don't match."
+        )
+        with self.assertRaisesMessage(AssertionError, msg) as ctx:
+            self.assertFormsetError(response, "formset", None, None, "error")
+        self.assertIn("[] != ['error']", str(ctx.exception))
+        msg_prefix = "Custom prefix"
+        with self.assertRaisesMessage(AssertionError, f"{msg_prefix}: {msg}"):
+            self.assertFormsetError(
+                response, "formset", None, None, "error", msg_prefix=msg_prefix
+            )
+
     def test_non_form_errors_with_field(self):
         response = mock.Mock(
             context=[