From 8bca838f4a230b78dd44fc1db3c1b81e444c6099 Mon Sep 17 00:00:00 2001
From: Chris Jerdonek <chris.jerdonek@gmail.com>
Date: Tue, 29 Jun 2021 13:02:57 -0400
Subject: [PATCH] Refs #32655 -- Improved error if iter_test_cases() is passed
 a string.

---
 django/test/utils.py       |  7 +++++++
 tests/test_runner/tests.py | 10 +++++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/django/test/utils.py b/django/test/utils.py
index e977db8a10..81005d4f8f 100644
--- a/django/test/utils.py
+++ b/django/test/utils.py
@@ -242,6 +242,13 @@ def iter_test_cases(tests):
     The tests argument can also be an iterable of TestCase objects.
     """
     for test in tests:
+        if isinstance(test, str):
+            # Prevent an unfriendly RecursionError that can happen with
+            # strings.
+            raise TypeError(
+                f'Test {test!r} must be a test case or test suite not string '
+                f'(was found in {tests!r}).'
+            )
         if isinstance(test, TestCase):
             yield test
         else:
diff --git a/tests/test_runner/tests.py b/tests/test_runner/tests.py
index 7479b80ef1..6348569dfc 100644
--- a/tests/test_runner/tests.py
+++ b/tests/test_runner/tests.py
@@ -36,7 +36,7 @@ class MySuite:
         yield from self.tests
 
 
-class TestSuiteTests(unittest.TestCase):
+class TestSuiteTests(SimpleTestCase):
     def build_test_suite(self, test_classes, suite=None, suite_class=None):
         if suite_class is None:
             suite_class = unittest.TestSuite
@@ -89,6 +89,14 @@ class TestSuiteTests(unittest.TestCase):
             'Tests1.test1', 'Tests1.test2', 'Tests2.test1', 'Tests2.test2',
         ])
 
+    def test_iter_test_cases_string_input(self):
+        msg = (
+            "Test 'a' must be a test case or test suite not string (was found "
+            "in 'abc')."
+        )
+        with self.assertRaisesMessage(TypeError, msg):
+            list(iter_test_cases('abc'))
+
     def test_iter_test_cases_iterable_of_tests(self):
         class Tests(unittest.TestCase):
             def test1(self):