From f525768167acf198b120a59ce9ac2f286a1677cb Mon Sep 17 00:00:00 2001
From: Ben Darnell <ben@bendarnell.com>
Date: Thu, 11 Jul 2024 15:21:09 -0400
Subject: [PATCH 1/5] test: Remove skipOnTravis

We haven't used Travis for CI in a long time, and our current CI
system is much less overloaded so these timing-sensitive tests are
no longer flaky.
---
 tornado/test/gen_test.py               | 3 +--
 tornado/test/httpclient_test.py        | 3 +--
 tornado/test/httpserver_test.py        | 3 +--
 tornado/test/ioloop_test.py            | 3 ---
 tornado/test/netutil_test.py           | 2 --
 tornado/test/simple_httpclient_test.py | 3 ---
 tornado/test/tcpclient_test.py         | 2 --
 tornado/test/util.py                   | 8 +-------
 8 files changed, 4 insertions(+), 23 deletions(-)

diff --git a/tornado/test/gen_test.py b/tornado/test/gen_test.py
index 87f6ab7fa4..1a365dbd72 100644
--- a/tornado/test/gen_test.py
+++ b/tornado/test/gen_test.py
@@ -11,7 +11,7 @@
 from tornado.concurrent import Future
 from tornado.log import app_log
 from tornado.testing import AsyncHTTPTestCase, AsyncTestCase, ExpectLog, gen_test
-from tornado.test.util import skipOnTravis, skipNotCPython
+from tornado.test.util import skipNotCPython
 from tornado.web import Application, RequestHandler, HTTPError
 
 from tornado import gen
@@ -139,7 +139,6 @@ def f():
 
         self.io_loop.run_sync(f)
 
-    @skipOnTravis
     @gen_test
     def test_multi_performance(self):
         # Yielding a list used to have quadratic performance; make
diff --git a/tornado/test/httpclient_test.py b/tornado/test/httpclient_test.py
index 40a29d0b9e..f6e7dbbe7f 100644
--- a/tornado/test/httpclient_test.py
+++ b/tornado/test/httpclient_test.py
@@ -28,7 +28,7 @@
 from tornado.log import gen_log, app_log
 from tornado import netutil
 from tornado.testing import AsyncHTTPTestCase, bind_unused_port, gen_test, ExpectLog
-from tornado.test.util import skipOnTravis, ignore_deprecation
+from tornado.test.util import ignore_deprecation
 from tornado.web import Application, RequestHandler, url
 from tornado.httputil import format_timestamp, HTTPHeaders
 
@@ -191,7 +191,6 @@ def test_patch_receives_payload(self):
         self.assertEqual(response.code, 200)
         self.assertEqual(response.body, body)
 
-    @skipOnTravis
     def test_hello_world(self):
         response = self.fetch("/hello")
         self.assertEqual(response.code, 200)
diff --git a/tornado/test/httpserver_test.py b/tornado/test/httpserver_test.py
index 3a90440dfc..7b411ed6e4 100644
--- a/tornado/test/httpserver_test.py
+++ b/tornado/test/httpserver_test.py
@@ -27,7 +27,7 @@
     ExpectLog,
     gen_test,
 )
-from tornado.test.util import skipOnTravis, abstract_base_test
+from tornado.test.util import abstract_base_test
 from tornado.web import Application, RequestHandler, stream_request_body
 
 from contextlib import closing
@@ -1267,7 +1267,6 @@ def test_large_headers(self):
                     self.assertIn(e.response.code, (431, 599))
 
 
-@skipOnTravis
 class IdleTimeoutTest(AsyncHTTPTestCase):
     def get_app(self):
         return Application([("/", HelloWorldRequestHandler)])
diff --git a/tornado/test/ioloop_test.py b/tornado/test/ioloop_test.py
index 2123939283..047b3614eb 100644
--- a/tornado/test/ioloop_test.py
+++ b/tornado/test/ioloop_test.py
@@ -28,7 +28,6 @@
 from tornado.test.util import (
     ignore_deprecation,
     skipIfNonUnix,
-    skipOnTravis,
 )
 from tornado.concurrent import Future
 
@@ -58,7 +57,6 @@ def add_callback(self, callback, *args, **kwargs):
         loop.start()
         self.assertLess(self.calls, 10)
 
-    @skipOnTravis
     def test_add_callback_wakeup(self):
         # Make sure that add_callback from inside a running IOLoop
         # wakes up the IOLoop immediately instead of waiting for a timeout.
@@ -77,7 +75,6 @@ def schedule_callback():
         self.assertAlmostEqual(time.time(), self.start_time, places=2)
         self.assertTrue(self.called)
 
-    @skipOnTravis
     def test_add_callback_wakeup_other_thread(self):
         def target():
             # sleep a bit to let the ioloop go into its poll loop
diff --git a/tornado/test/netutil_test.py b/tornado/test/netutil_test.py
index ef82cba85f..2334727873 100644
--- a/tornado/test/netutil_test.py
+++ b/tornado/test/netutil_test.py
@@ -188,8 +188,6 @@ def test_is_valid_ip(self):
 
 class TestPortAllocation(unittest.TestCase):
     def test_same_port_allocation(self):
-        if "TRAVIS" in os.environ:
-            self.skipTest("dual-stack servers often have port conflicts on travis")
         sockets = bind_sockets(0, "localhost")
         try:
             port = sockets[0].getsockname()[1]
diff --git a/tornado/test/simple_httpclient_test.py b/tornado/test/simple_httpclient_test.py
index 07f04ae938..c1cff83c9a 100644
--- a/tornado/test/simple_httpclient_test.py
+++ b/tornado/test/simple_httpclient_test.py
@@ -41,7 +41,6 @@
 )
 from tornado.test.util import (
     abstract_base_test,
-    skipOnTravis,
     skipIfNoIPv6,
     refusing_port,
 )
@@ -288,7 +287,6 @@ def test_see_other_redirect(self):
             # request is the original request, is a POST still
             self.assertEqual("POST", response.request.method)
 
-    @skipOnTravis
     @gen_test
     def test_connect_timeout(self):
         timeout = 0.1
@@ -317,7 +315,6 @@ async def resolve(self, *args, **kwargs):
         cleanup_event.set()
         yield gen.sleep(0.2)
 
-    @skipOnTravis
     def test_request_timeout(self):
         timeout = 0.1
         if os.name == "nt":
diff --git a/tornado/test/tcpclient_test.py b/tornado/test/tcpclient_test.py
index 1636a649b8..73b383cbab 100644
--- a/tornado/test/tcpclient_test.py
+++ b/tornado/test/tcpclient_test.py
@@ -64,8 +64,6 @@ def setUp(self):
         self.client = TCPClient()
 
     def start_server(self, family):
-        if family == socket.AF_UNSPEC and "TRAVIS" in os.environ:
-            self.skipTest("dual-stack servers often have port conflicts on travis")
         self.server = TestTCPServer(family)
         return self.server.port
 
diff --git a/tornado/test/util.py b/tornado/test/util.py
index 40ff9d65e6..2e8bc3e5f1 100644
--- a/tornado/test/util.py
+++ b/tornado/test/util.py
@@ -16,12 +16,6 @@
     os.name != "posix" or sys.platform == "cygwin", "non-unix platform"
 )
 
-# travis-ci.org runs our tests in an overworked virtual machine, which makes
-# timing-related tests unreliable.
-skipOnTravis = unittest.skipIf(
-    "TRAVIS" in os.environ, "timing tests unreliable on travis"
-)
-
 # Set the environment variable NO_NETWORK=1 to disable any tests that
 # depend on an external network.
 skipIfNoNetwork = unittest.skipIf("NO_NETWORK" in os.environ, "network access disabled")
@@ -67,7 +61,7 @@ def refusing_port():
     Return value is (cleanup_func, port); the cleanup function
     must be called to free the port to be reused.
     """
-    # On travis-ci, port numbers are reassigned frequently. To avoid
+    # On travis-ci port numbers are reassigned frequently. To avoid
     # collisions with other tests, we use an open client-side socket's
     # ephemeral port number to ensure that nothing can listen on that
     # port.

From 1808129122f81b0e78120c29233381be5c37b0b8 Mon Sep 17 00:00:00 2001
From: Ben Darnell <ben@bendarnell.com>
Date: Thu, 11 Jul 2024 15:26:14 -0400
Subject: [PATCH 2/5] test: Remove some obsolete checks for old python versions

---
 tornado/test/gen_test.py       |  3 ---
 tornado/test/iostream_test.py  |  3 ---
 tornado/test/netutil_test.py   |  1 -
 tornado/test/tcpclient_test.py |  1 -
 tornado/test/util.py           | 10 ----------
 5 files changed, 18 deletions(-)

diff --git a/tornado/test/gen_test.py b/tornado/test/gen_test.py
index 1a365dbd72..ec3a6c8e69 100644
--- a/tornado/test/gen_test.py
+++ b/tornado/test/gen_test.py
@@ -572,9 +572,6 @@ def inner(iteration):
         self.finished = True
 
     @skipNotCPython
-    @unittest.skipIf(
-        (3,) < sys.version_info < (3, 6), "asyncio.Future has reference cycles"
-    )
     def test_coroutine_refcounting(self):
         # On CPython, tasks and their arguments should be released immediately
         # without waiting for garbage collection.
diff --git a/tornado/test/iostream_test.py b/tornado/test/iostream_test.py
index 200b08303f..09191ecfef 100644
--- a/tornado/test/iostream_test.py
+++ b/tornado/test/iostream_test.py
@@ -27,7 +27,6 @@
 from tornado.test.util import (
     skipIfNonUnix,
     refusing_port,
-    skipPypy3V58,
     ignore_deprecation,
     abstract_base_test,
 )
@@ -828,7 +827,6 @@ def test_read_until_close_with_error(self):
             client.close()
 
     @skipIfNonUnix
-    @skipPypy3V58
     @gen_test
     def test_inline_read_error(self):
         # An error on an inline read is raised without logging (on the
@@ -862,7 +860,6 @@ def test_inline_read_error(self):
             server.close()
             client.close()
 
-    @skipPypy3V58
     @gen_test
     def test_async_read_error_logging(self):
         # Socket errors on asynchronous reads should be logged (but only
diff --git a/tornado/test/netutil_test.py b/tornado/test/netutil_test.py
index 2334727873..117a9d7f99 100644
--- a/tornado/test/netutil_test.py
+++ b/tornado/test/netutil_test.py
@@ -1,5 +1,4 @@
 import errno
-import os
 import signal
 import socket
 from subprocess import Popen
diff --git a/tornado/test/tcpclient_test.py b/tornado/test/tcpclient_test.py
index 73b383cbab..5638559cec 100644
--- a/tornado/test/tcpclient_test.py
+++ b/tornado/test/tcpclient_test.py
@@ -14,7 +14,6 @@
 # under the License.
 from contextlib import closing
 import getpass
-import os
 import socket
 import unittest
 
diff --git a/tornado/test/util.py b/tornado/test/util.py
index 2e8bc3e5f1..ed5fd5d3f6 100644
--- a/tornado/test/util.py
+++ b/tornado/test/util.py
@@ -24,16 +24,6 @@
     platform.python_implementation() != "CPython", "Not CPython implementation"
 )
 
-# Used for tests affected by
-# https://bitbucket.org/pypy/pypy/issues/2616/incomplete-error-handling-in
-# TODO: remove this after pypy3 5.8 is obsolete.
-skipPypy3V58 = unittest.skipIf(
-    platform.python_implementation() == "PyPy"
-    and sys.version_info > (3,)
-    and sys.pypy_version_info < (5, 9),  # type: ignore
-    "pypy3 5.8 has buggy ssl module",
-)
-
 
 def _detect_ipv6():
     if not socket.has_ipv6:

From 00110e1602c516d2dcb371c5b9aa92b522ee7c48 Mon Sep 17 00:00:00 2001
From: Ben Darnell <ben@bendarnell.com>
Date: Thu, 11 Jul 2024 15:43:32 -0400
Subject: [PATCH 3/5] *: Remove references to old python versions

Mainly in docs that say things like "you can only use this if you're
using python 3.2".
---
 tornado/gen.py                | 15 ++++++---------
 tornado/iostream.py           |  9 +--------
 tornado/netutil.py            | 18 ++++++------------
 tornado/options.py            | 17 ++++++-----------
 tornado/tcpserver.py          |  2 +-
 tornado/test/__main__.py      |  2 --
 tornado/test/gen_test.py      |  1 -
 tornado/test/iostream_test.py |  2 --
 tornado/test/web_test.py      | 10 +++-------
 9 files changed, 23 insertions(+), 53 deletions(-)

diff --git a/tornado/gen.py b/tornado/gen.py
index 51fa4c19ae..d12f32fbd8 100644
--- a/tornado/gen.py
+++ b/tornado/gen.py
@@ -275,6 +275,10 @@ def is_coroutine_function(func: Any) -> bool:
 class Return(Exception):
     """Special exception to return a value from a `coroutine`.
 
+    This exception exists for compatibility with older versions of
+    Python (before 3.3). In newer code use the ``return`` statement
+    instead.
+
     If this exception is raised, its value argument is used as the
     result of the coroutine::
 
@@ -283,14 +287,7 @@ def fetch_json(url):
             response = yield AsyncHTTPClient().fetch(url)
             raise gen.Return(json_decode(response.body))
 
-    In Python 3.3, this exception is no longer necessary: the ``return``
-    statement can be used directly to return a value (previously
-    ``yield`` and ``return`` with a value could not be combined in the
-    same function).
-
-    By analogy with the return statement, the value argument is optional,
-    but it is never necessary to ``raise gen.Return()``.  The ``return``
-    statement can be used with no arguments instead.
+    By analogy with the return statement, the value argument is optional.
     """
 
     def __init__(self, value: Any = None) -> None:
@@ -337,7 +334,7 @@ class WaitIterator:
     arguments were used in the construction of the `WaitIterator`,
     ``current_index`` will use the corresponding keyword).
 
-    On Python 3.5, `WaitIterator` implements the async iterator
+    `WaitIterator` implements the async iterator
     protocol, so it can be used with the ``async for`` statement (note
     that in this version the entire iteration is aborted if any value
     raises an exception, while the previous example can continue past
diff --git a/tornado/iostream.py b/tornado/iostream.py
index 40b4f8d4e7..dd2111e3b8 100644
--- a/tornado/iostream.py
+++ b/tornado/iostream.py
@@ -1147,8 +1147,7 @@ class is recommended instead of calling this method directly.
 
         In SSL mode, the ``server_hostname`` parameter will be used
         for certificate validation (unless disabled in the
-        ``ssl_options``) and SNI (if supported; requires Python
-        2.7.9+).
+        ``ssl_options``) and SNI.
 
         Note that it is safe to call `IOStream.write
         <BaseIOStream.write>` while the connection is pending, in
@@ -1381,12 +1380,6 @@ def _do_ssl_handshake(self) -> None:
                 )
                 return self.close(exc_info=err)
             raise
-        except ssl.CertificateError as err:
-            # CertificateError can happen during handshake (hostname
-            # verification) and should be passed to user. Starting
-            # in Python 3.7, this error is a subclass of SSLError
-            # and will be handled by the previous block instead.
-            return self.close(exc_info=err)
         except OSError as err:
             # Some port scans (e.g. nmap in -sT mode) have been known
             # to cause do_handshake to raise EBADF and ENOTCONN, so make
diff --git a/tornado/netutil.py b/tornado/netutil.py
index b6772086af..3ec76af77c 100644
--- a/tornado/netutil.py
+++ b/tornado/netutil.py
@@ -501,10 +501,6 @@ def initialize(self) -> None:  # type: ignore
 class ThreadedResolver(ExecutorResolver):
     """Multithreaded non-blocking `Resolver` implementation.
 
-    Requires the `concurrent.futures` package to be installed
-    (available in the standard library since Python 3.2,
-    installable with ``pip install futures`` in older versions).
-
     The thread pool size can be configured with::
 
         Resolver.configure('tornado.netutil.ThreadedResolver',
@@ -598,17 +594,15 @@ def ssl_options_to_context(
     """Try to convert an ``ssl_options`` dictionary to an
     `~ssl.SSLContext` object.
 
-    The ``ssl_options`` dictionary contains keywords to be passed to
-    ``ssl.SSLContext.wrap_socket``.  In Python 2.7.9+, `ssl.SSLContext` objects can
-    be used instead.  This function converts the dict form to its
-    `~ssl.SSLContext` equivalent, and may be used when a component which
-    accepts both forms needs to upgrade to the `~ssl.SSLContext` version
-    to use features like SNI or NPN.
+    The ``ssl_options`` argument may be either an `ssl.SSLContext` object or a dictionary containing
+    keywords to be passed to ``ssl.SSLContext.wrap_socket``.  This function converts the dict form
+    to its `~ssl.SSLContext` equivalent, and may be used when a component which accepts both forms
+    needs to upgrade to the `~ssl.SSLContext` version to use features like SNI or ALPN.
 
     .. versionchanged:: 6.2
 
-       Added server_side argument. Omitting this argument will
-       result in a DeprecationWarning on Python 3.10.
+       Added server_side argument. Omitting this argument will result in a DeprecationWarning on
+       Python 3.10.
 
     """
     if isinstance(ssl_options, ssl.SSLContext):
diff --git a/tornado/options.py b/tornado/options.py
index d02a730c6a..b6578bb901 100644
--- a/tornado/options.py
+++ b/tornado/options.py
@@ -482,15 +482,11 @@ def run_parse_callbacks(self) -> None:
 
     def mockable(self) -> "_Mockable":
         """Returns a wrapper around self that is compatible with
-        `mock.patch <unittest.mock.patch>`.
+        `unittest.mock.patch`.
 
-        The `mock.patch <unittest.mock.patch>` function (included in
-        the standard library `unittest.mock` package since Python 3.3,
-        or in the third-party ``mock`` package for older versions of
-        Python) is incompatible with objects like ``options`` that
-        override ``__getattr__`` and ``__setattr__``.  This function
-        returns an object that can be used with `mock.patch.object
-        <unittest.mock.patch.object>` to modify option values::
+        The `unittest.mock.patch` function is incompatible with objects like ``options`` that
+        override ``__getattr__`` and ``__setattr__``.  This function returns an object that can be
+        used with `mock.patch.object <unittest.mock.patch.object>` to modify option values::
 
             with mock.patch.object(options.mockable(), 'name', value):
                 assert options.name == value
@@ -664,9 +660,8 @@ def _parse_timedelta(self, value: str) -> datetime.timedelta:
                 num = float(m.group(1))
                 units = m.group(2) or "seconds"
                 units = self._TIMEDELTA_ABBREV_DICT.get(units, units)
-                # This line confuses mypy when setup.py sets python_version=3.6
-                # https://github.com/python/mypy/issues/9676
-                sum += datetime.timedelta(**{units: num})  # type: ignore
+
+                sum += datetime.timedelta(**{units: num})
                 start = m.end()
             return sum
         except Exception:
diff --git a/tornado/tcpserver.py b/tornado/tcpserver.py
index a9ae88def7..6d74224b76 100644
--- a/tornado/tcpserver.py
+++ b/tornado/tcpserver.py
@@ -339,7 +339,7 @@ def handle_stream(
 
     def _handle_connection(self, connection: socket.socket, address: Any) -> None:
         if self.ssl_options is not None:
-            assert ssl, "Python 2.6+ and OpenSSL required for SSL"
+            assert ssl, "OpenSSL required for SSL"
             try:
                 connection = ssl_wrap_socket(
                     connection,
diff --git a/tornado/test/__main__.py b/tornado/test/__main__.py
index 890bd505b4..65b794d9be 100644
--- a/tornado/test/__main__.py
+++ b/tornado/test/__main__.py
@@ -1,6 +1,4 @@
 """Shim to allow python -m tornado.test.
-
-This only works in python 2.7+.
 """
 
 from tornado.test.runtests import all, main
diff --git a/tornado/test/gen_test.py b/tornado/test/gen_test.py
index ec3a6c8e69..71fdceb1c9 100644
--- a/tornado/test/gen_test.py
+++ b/tornado/test/gen_test.py
@@ -441,7 +441,6 @@ def f():
 
     @gen_test
     def test_async_return_no_value(self):
-        # Without a return value we don't need python 3.3.
         @gen.coroutine
         def f():
             yield gen.moment
diff --git a/tornado/test/iostream_test.py b/tornado/test/iostream_test.py
index 09191ecfef..d55485c70d 100644
--- a/tornado/test/iostream_test.py
+++ b/tornado/test/iostream_test.py
@@ -1078,8 +1078,6 @@ def test_handshake_fail(self):
     @gen_test
     def test_check_hostname(self):
         # Test that server_hostname parameter to start_tls is being used.
-        # The check_hostname functionality is only available in python 2.7 and
-        # up and in python 3.4 and up.
         server_future = self.server_start_tls(_server_ssl_options())
         with ExpectLog(gen_log, "SSL Error"):
             client_future = self.client_start_tls(
diff --git a/tornado/test/web_test.py b/tornado/test/web_test.py
index 32a12bad99..7e1278e6c3 100644
--- a/tornado/test/web_test.py
+++ b/tornado/test/web_test.py
@@ -367,7 +367,7 @@ def test_cookie_special_char(self):
         self.assertEqual(len(headers), 3)
         self.assertEqual(headers[0], 'equals="a=b"; Path=/')
         self.assertEqual(headers[1], 'quote="a\\"b"; Path=/')
-        # python 2.7 octal-escapes the semicolon; older versions leave it alone
+        # Semicolons are octal-escaped
         self.assertIn(
             headers[2],
             ('semicolon="a;b"; Path=/', 'semicolon="a\\073b"; Path=/'),
@@ -1888,12 +1888,8 @@ def test_clear_all_cookies(self):
         response = self.fetch("/", headers={"Cookie": "foo=bar; baz=xyzzy"})
         set_cookies = sorted(response.headers.get_list("Set-Cookie"))
         # Python 3.5 sends 'baz="";'; older versions use 'baz=;'
-        self.assertTrue(
-            set_cookies[0].startswith("baz=;") or set_cookies[0].startswith('baz="";')
-        )
-        self.assertTrue(
-            set_cookies[1].startswith("foo=;") or set_cookies[1].startswith('foo="";')
-        )
+        self.assertTrue(set_cookies[0].startswith('baz="";'))
+        self.assertTrue(set_cookies[1].startswith('foo="";'))
 
 
 class PermissionError(Exception):

From ef8c6ab9bb14a4a966f052c27b9b63a7064e7f3f Mon Sep 17 00:00:00 2001
From: Ben Darnell <ben@bendarnell.com>
Date: Thu, 11 Jul 2024 15:46:50 -0400
Subject: [PATCH 4/5] web_test: Remove obsolete compatibility with python 3.4

---
 tornado/test/web_test.py | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/tornado/test/web_test.py b/tornado/test/web_test.py
index 7e1278e6c3..d43ea78dd2 100644
--- a/tornado/test/web_test.py
+++ b/tornado/test/web_test.py
@@ -417,12 +417,10 @@ def test_set_cookie_expires_days(self):
     def test_set_cookie_false_flags(self):
         response = self.fetch("/set_falsy_flags")
         headers = sorted(response.headers.get_list("Set-Cookie"))
-        # The secure and httponly headers are capitalized in py35 and
-        # lowercase in older versions.
-        self.assertEqual(headers[0].lower(), "a=1; path=/; secure")
-        self.assertEqual(headers[1].lower(), "b=1; path=/")
-        self.assertEqual(headers[2].lower(), "c=1; httponly; path=/")
-        self.assertEqual(headers[3].lower(), "d=1; path=/")
+        self.assertEqual(headers[0], "a=1; Path=/; Secure")
+        self.assertEqual(headers[1], "b=1; Path=/")
+        self.assertEqual(headers[2], "c=1; HttpOnly; Path=/")
+        self.assertEqual(headers[3], "d=1; Path=/")
 
     def test_set_cookie_deprecated(self):
         with ignore_deprecation():

From 77e0a4f9cf8ccc4654afa4ef769fb1c5e4c12133 Mon Sep 17 00:00:00 2001
From: Ben Darnell <ben@bendarnell.com>
Date: Thu, 11 Jul 2024 15:50:21 -0400
Subject: [PATCH 5/5] test.util: Remove our private compatibility shim for
 subTests

---
 tornado/test/options_test.py |  3 +--
 tornado/test/util.py         | 12 ------------
 2 files changed, 1 insertion(+), 14 deletions(-)

diff --git a/tornado/test/options_test.py b/tornado/test/options_test.py
index 99c3c12c80..67d89c250e 100644
--- a/tornado/test/options_test.py
+++ b/tornado/test/options_test.py
@@ -7,7 +7,6 @@
 
 from tornado.options import OptionParser, Error
 from tornado.util import basestring_type
-from tornado.test.util import subTest
 
 import typing
 
@@ -277,7 +276,7 @@ def test_error_redefine_underscore(self):
             ("foo_bar", "foo-bar"),
         ]
         for a, b in tests:
-            with subTest(self, a=a, b=b):
+            with self.subTest(self, a=a, b=b):
                 options = OptionParser()
                 options.define(a)
                 with self.assertRaises(Error) as cm:
diff --git a/tornado/test/util.py b/tornado/test/util.py
index ed5fd5d3f6..25dd2000fd 100644
--- a/tornado/test/util.py
+++ b/tornado/test/util.py
@@ -80,18 +80,6 @@ def exec_test(caller_globals, caller_locals, s):
     return local_namespace
 
 
-def subTest(test, *args, **kwargs):
-    """Compatibility shim for unittest.TestCase.subTest.
-
-    Usage: ``with tornado.test.util.subTest(self, x=x):``
-    """
-    try:
-        subTest = test.subTest  # py34+
-    except AttributeError:
-        subTest = contextlib.contextmanager(lambda *a, **kw: (yield))
-    return subTest(*args, **kwargs)
-
-
 @contextlib.contextmanager
 def ignore_deprecation():
     """Context manager to ignore deprecation warnings."""