Index: tornado-6.4/tornado/util.py
===================================================================
--- tornado-6.4.orig/tornado/util.py
+++ tornado-6.4/tornado/util.py
@@ -458,5 +458,7 @@ else:
 def doctests():
     # type: () -> unittest.TestSuite
     import doctest
+    import warnings
+    warnings.simplefilter("ignore", ResourceWarning)
 
     return doctest.DocTestSuite()
Index: tornado-6.4/tornado/httputil.py
===================================================================
--- tornado-6.4.orig/tornado/httputil.py
+++ tornado-6.4/tornado/httputil.py
@@ -1020,6 +1020,8 @@ def encode_username_password(
 def doctests():
     # type: () -> unittest.TestSuite
     import doctest
+    import warnings
+    warnings.simplefilter("ignore", ResourceWarning)
 
     return doctest.DocTestSuite()
 
Index: tornado-6.4/tornado/iostream.py
===================================================================
--- tornado-6.4.orig/tornado/iostream.py
+++ tornado-6.4/tornado/iostream.py
@@ -1623,5 +1623,7 @@ class PipeIOStream(BaseIOStream):
 
 def doctests() -> Any:
     import doctest
+    import warnings
+    warnings.simplefilter("ignore", ResourceWarning)
 
     return doctest.DocTestSuite()