Fixed #19546 - ensure that deprecation warnings are shown during tests

refs #18985

tests/regressiontests/test_runner/deprecation_app/tests.py

@@ -0,0 +1,9 @@
+import warnings
+
+from django.test import TestCase
+
+class DummyTest(TestCase):
+    def test_warn(self):
+        warnings.warn("warning from test", DeprecationWarning)
+
+