Issue #23738: Document and test actual keyword parameter names

Also fix signature because os.utime(..., ns=None) is not allowed.

Lib/test/test_os.py

@@ -58,7 +58,7 @@ HAVE_WHEEL_GROUP = sys.platform.startswith('freebsd') and os.getgid() == 0
 # Tests creating TESTFN
 class FileTests(unittest.TestCase):
     def setUp(self):
-        if os.path.exists(support.TESTFN):
+        if os.path.lexists(support.TESTFN):
             os.unlink(support.TESTFN)
     tearDown = setUp
 
@@ -162,6 +162,19 @@ class FileTests(unittest.TestCase):
         with open(TESTFN2, 'r') as f:
             self.assertEqual(f.read(), "1")
 
+    def test_open_keywords(self):
+        f = os.open(path=__file__, flags=os.O_RDONLY, mode=0o777,
+            dir_fd=None)
+        os.close(f)
+
+    def test_symlink_keywords(self):
+        symlink = support.get_attribute(os, "symlink")
+        try:
+            symlink(src='target', dst=support.TESTFN,
+                target_is_directory=False, dir_fd=None)
+        except (NotImplementedError, OSError):
+            pass  # No OS support or unprivileged user
+
 
 # Test attributes on return values from os.*stat* family.
 class StatAttributeTests(unittest.TestCase):
@@ -2151,6 +2164,14 @@ class TestSendfile(unittest.TestCase):
             os.sendfile(self.sockno, self.fileno, -1, 4096)
         self.assertEqual(cm.exception.errno, errno.EINVAL)
 
+    def test_keywords(self):
+        # Keyword arguments should be supported
+        os.sendfile(out=self.sockno, offset=0, count=4096,
+            **{'in': self.fileno})
+        if self.SUPPORT_HEADERS_TRAILERS:
+            os.sendfile(self.sockno, self.fileno, offset=0, count=4096,
+                headers=None, trailers=None, flags=0)
+
     # --- headers / trailers tests
 
     @requires_headers_trailers