unittest: Print an error message if no tests ran

Author: stefanor

Lib/test/test_unittest/test_runner.py

@@ -574,6 +574,16 @@ def test(self):
                 'inner setup', 'inner test', 'inner cleanup',
                 'end outer test', 'outer cleanup'])
 
+    def test_run_empty_suite_error_message(self):
+        class EmptyTest(unittest.TestCase):
+            pass
+
+        suite = unittest.defaultTestLoader.loadTestsFromTestCase(EmptyTest)
+        runner = getRunner()
+        runner.run(suite)
+
+        self.assertIn("\nNO TESTS RUN\n", runner.stream.getvalue())
+
 
 class TestModuleCleanUp(unittest.TestCase):
     def test_add_and_do_ModuleCleanup(self):

Lib/unittest/runner.py

@@ -238,6 +238,8 @@ def run(self, test):
                 infos.append("failures=%d" % failed)
             if errored:
                 infos.append("errors=%d" % errored)
+        elif run == 0:
+            self.stream.write("NO TESTS RUN")
         else:
             self.stream.write("OK")
         if skipped: