Fix duplicate_iterators for async spies

CHANGELOG.rst

@@ -4,6 +4,7 @@ Releases
 Unreleased
 ----------
 
+* Fixed ``duplicate_iterators=True`` for async functions spied with ``mocker.spy``.
 * `#547 <https://github.com/pytest-dev/pytest-mock/issues/547>`_: Added ``SpyType`` for annotating ``mocker.spy`` results.
 * Dropped support for EOL Python 3.9.
 * `#147 <https://github.com/pytest-dev/pytest-mock/issues/147>`_: Removed handling of ``RuntimeError: stop called on unstarted patcher``, which can no longer occur in the supported Python versions.

src/pytest_mock/plugin.py

@@ -206,6 +206,12 @@ async def async_wrapper(*args, **kwargs):
                 spy_obj.spy_exception = e
                 raise
             else:
+                if duplicate_iterators and isinstance(r, Iterator):
+                    r, duplicated_iterator = itertools.tee(r, 2)
+                    spy_obj.spy_return_iter = duplicated_iterator
+                else:
+                    spy_obj.spy_return_iter = None
+
                 spy_obj.spy_return = r
                 spy_obj.spy_return_list.append(r)
             return r

tests/test_pytest_mock.py

@@ -666,6 +666,27 @@ async def bar(self, arg):
     assert result == 20
 
 
+@pytest.mark.asyncio
+async def test_async_spy_return_iter_duplicates_iterator_when_enabled(
+    mocker: MockerFixture,
+) -> None:
+    class Foo:
+        async def bar(self) -> Iterator[int]:
+            return iter([0, 1, 2])
+
+    foo = Foo()
+    spy = mocker.spy(foo, "bar", duplicate_iterators=True)
+    result = await foo.bar()
+
+    assert list(result) == [0, 1, 2]
+    assert spy.spy_return is not None
+    assert spy.spy_return_iter is not None
+    assert list(spy.spy_return_iter) == [0, 1, 2]
+
+    [return_value] = spy.spy_return_list
+    assert isinstance(return_value, Iterator)
+
+
 @contextmanager
 def assert_traceback() -> Generator[None, None, None]:
     """