1 files changed, 64 insertions, 41 deletions
diff --git a/lib/sqlalchemy/testing/assertions.py b/lib/sqlalchemy/testing/assertions.py
index 0cf0cbc7a..986dbb5e9 100644
--- a/lib/sqlalchemy/testing/assertions.py
+++ b/lib/sqlalchemy/testing/assertions.py
@@ -133,6 +133,11 @@ def uses_deprecated(*messages):
     return decorate
 
 
+_FILTERS = None
+_SEEN = None
+_EXC_CLS = None
+
+
 @contextlib.contextmanager
 def _expect_warnings(
     exc_cls,
@@ -143,58 +148,76 @@ def _expect_warnings(
     raise_on_any_unexpected=False,
 ):
 
+    global _FILTERS, _SEEN, _EXC_CLS
+
     if regex:
         filters = [re.compile(msg, re.I | re.S) for msg in messages]
     else:
-        filters = messages
-
-    seen = set(filters)
+        filters = list(messages)
+
+    if _FILTERS is not None:
+        # nested call; update _FILTERS and _SEEN, return.  outer
+        # block will assert our messages
+        assert _SEEN is not None
+        assert _EXC_CLS is not None
+        _FILTERS.extend(filters)
+        _SEEN.update(filters)
+        _EXC_CLS += (exc_cls,)
+        yield
+    else:
+        seen = _SEEN = set(filters)
+        _FILTERS = filters
+        _EXC_CLS = (exc_cls,)
 
-    if raise_on_any_unexpected:
+        if raise_on_any_unexpected:
 
-        def real_warn(msg, *arg, **kw):
-            raise AssertionError("Got unexpected warning: %r" % msg)
+            def real_warn(msg, *arg, **kw):
+                raise AssertionError("Got unexpected warning: %r" % msg)
 
-    else:
-        real_warn = warnings.warn
-
-    def our_warn(msg, *arg, **kw):
-        if isinstance(msg, exc_cls):
-            exception = type(msg)
-            msg = str(msg)
-        elif arg:
-            exception = arg[0]
         else:
-            exception = None
+            real_warn = warnings.warn
 
-        if not exception or not issubclass(exception, exc_cls):
-            return real_warn(msg, *arg, **kw)
+        def our_warn(msg, *arg, **kw):
 
-        if not filters and not raise_on_any_unexpected:
-            return
+            if isinstance(msg, _EXC_CLS):
+                exception = type(msg)
+                msg = str(msg)
+            elif arg:
+                exception = arg[0]
+            else:
+                exception = None
 
-        for filter_ in filters:
-            if (regex and filter_.match(msg)) or (
-                not regex and filter_ == msg
-            ):
-                seen.discard(filter_)
-                break
-        else:
-            real_warn(msg, *arg, **kw)
-
-    with mock.patch("warnings.warn", our_warn), mock.patch(
-        "sqlalchemy.util.SQLALCHEMY_WARN_20", True
-    ), mock.patch(
-        "sqlalchemy.util.deprecations.SQLALCHEMY_WARN_20", True
-    ), mock.patch(
-        "sqlalchemy.engine.row.LegacyRow._default_key_style", 2
-    ):
-        yield
+            if not exception or not issubclass(exception, _EXC_CLS):
+                return real_warn(msg, *arg, **kw)
 
-    if assert_ and (not py2konly or not compat.py3k):
-        assert not seen, "Warnings were not seen: %s" % ", ".join(
-            "%r" % (s.pattern if regex else s) for s in seen
-        )
+            if not filters and not raise_on_any_unexpected:
+                return
+
+            for filter_ in filters:
+                if (regex and filter_.match(msg)) or (
+                    not regex and filter_ == msg
+                ):
+                    seen.discard(filter_)
+                    break
+            else:
+                real_warn(msg, *arg, **kw)
+
+        with mock.patch("warnings.warn", our_warn), mock.patch(
+            "sqlalchemy.util.SQLALCHEMY_WARN_20", True
+        ), mock.patch(
+            "sqlalchemy.util.deprecations.SQLALCHEMY_WARN_20", True
+        ), mock.patch(
+            "sqlalchemy.engine.row.LegacyRow._default_key_style", 2
+        ):
+            try:
+                yield
+            finally:
+                _SEEN = _FILTERS = _EXC_CLS = None
+
+                if assert_ and (not py2konly or not compat.py3k):
+                    assert not seen, "Warnings were not seen: %s" % ", ".join(
+                        "%r" % (s.pattern if regex else s) for s in seen
+                    )
 
 
 def global_cleanup_assertions():