Fixed #32360 -- Added system check for FILE_UPLOAD_TEMP_DIR setting.

tests/check_framework/test_files.py

@@ -0,0 +1,32 @@
+from pathlib import Path
+
+from django.core.checks import Error
+from django.core.checks.files import check_setting_file_upload_temp_dir
+from django.test import SimpleTestCase
+
+
+class FilesCheckTests(SimpleTestCase):
+    def test_file_upload_temp_dir(self):
+        tests = [
+            None,
+            '',
+            Path.cwd(),
+            str(Path.cwd()),
+        ]
+        for setting in tests:
+            with self.subTest(setting), self.settings(FILE_UPLOAD_TEMP_DIR=setting):
+                self.assertEqual(check_setting_file_upload_temp_dir(None), [])
+
+    def test_file_upload_temp_dir_nonexistent(self):
+        for setting in ['nonexistent', Path('nonexistent')]:
+            with self.subTest(setting), self.settings(FILE_UPLOAD_TEMP_DIR=setting):
+                self.assertEqual(
+                    check_setting_file_upload_temp_dir(None),
+                    [
+                        Error(
+                            "The FILE_UPLOAD_TEMP_DIR setting refers to the "
+                            "nonexistent directory 'nonexistent'.",
+                            id='files.E001',
+                        ),
+                    ],
+                )