testing: allow to instantiate an empty AsyncTestCase

tornado/test/testing_test.py

@@ -61,6 +61,15 @@ def test_subsequent_wait_calls(self):
  self.io_loop.add_timeout(self.io_loop.time() + 0.2, self.stop)
  self.wait(timeout=0.4)
 
+ def test_empty_instantation_is_allowed(self):
+ """
+ Test that empty instatiation of an AsyncTestCase is allowed.
+
+ unittest.TestCase docs guarantee this working, and pytest's unittest
+ support relies on it.
+ """
+ AsyncTestCaseTest()
+
 
 class LeakTest(AsyncTestCase):
  def tearDown(self):

tornado/testing.py

@@ -177,7 +177,17 @@ def __init__(self, methodName: str = "runTest") -> None:
  # the test will silently be ignored because nothing will consume
  # the generator. Replace the test method with a wrapper that will
  # make sure it's not an undecorated generator.
- setattr(self, methodName, _TestMethodWrapper(getattr(self, methodName)))
+ try:
+ test_method = getattr(self, methodName)
+ except AttributeError:
+ if methodName != "runTest":
+ # We allow instantiation with no explicit method name
+ # but not an *incorrect* or missing method name.
+ raise ValueError(
+ "no such test method in %s: %s" % (self.__class__, methodName)
+ )
+ else:
+ setattr(self, methodName, _TestMethodWrapper(test_method))
 
  # Not used in this class itself, but used by @gen_test
  self._test_generator = None # type: Optional[Union[Generator, Coroutine]]