Add tests for valid/invalid file with stdout/err as None

Author: ptim0626

Lib/test/test_argparse.py

@@ -79,6 +79,60 @@ def test_skip_invalid_stdout(self):
                 func()
                 self.assertRegex(mocked_stderr.getvalue(), r'usage:')
 
+    def test_invalid_file_only(self):
+        parser = argparse.ArgumentParser()
+        for func in (
+            parser.print_usage,
+            parser.print_help,
+        ):
+            self.assertRaises(ValueError, func, "invalid file")
+
+    def test_valid_file_invalid_stdout(self):
+        parser = argparse.ArgumentParser()
+        for func in (
+            parser.print_usage,
+            parser.print_help,
+        ):
+            with (
+                self.subTest(func=func),
+                contextlib.redirect_stdout(None),
+                StdIOBuffer() as f,
+                mock.patch('argparse._sys.exit'),
+            ):
+                func(file=f)
+                self.assertRegex(f.getvalue(), r'usage:')
+
+    def test_valid_file_invalid_stderr(self):
+        parser = argparse.ArgumentParser()
+        for func in (
+            parser.print_usage,
+            parser.print_help,
+        ):
+            with (
+                self.subTest(func=func),
+                contextlib.redirect_stderr(None),
+                StdIOBuffer() as f,
+                mock.patch('argparse._sys.exit'),
+            ):
+                func(file=f)
+                self.assertRegex(f.getvalue(), r'usage:')
+
+    def test_valid_file_invalid_stdout_stderr(self):
+        parser = argparse.ArgumentParser()
+        for func in (
+            parser.print_usage,
+            parser.print_help,
+        ):
+            with (
+                self.subTest(func=func),
+                contextlib.redirect_stdout(None),
+                contextlib.redirect_stderr(None),
+                StdIOBuffer() as f,
+                mock.patch('argparse._sys.exit'),
+            ):
+                func(file=f)
+                self.assertRegex(f.getvalue(), r'usage:')
+
 
 class TestLazyImports(unittest.TestCase):
     LAZY_IMPORTS = {