test.util: Remove our private compatibility shim for subTests

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:

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."""