Fix duplicate_iterators for async spies (#604)

mocker.spy supports async functions and documents spy_return_iter for iterator returns when duplicate_iterators=True. The synchronous spy wrapper honors that option, but the async wrapper returned the original iterator without creating the duplicate, leaving spy_return_iter as None.

---------

Co-authored-by: Bruno Oliveira <bruno@soliv.dev>

Author: lprnmns

CHANGELOG.rst

@@ -4,9 +4,8 @@ Releases
 Unreleased
 ----------
 
+* `#604 <https://github.com/pytest-dev/pytest-mock/pull/604>`_: Fixed ``duplicate_iterators=True`` for async functions spied with ``mocker.spy``.
 * `#611 <https://github.com/pytest-dev/pytest-mock/pull/611>`_: Fixed async mock assertion introspection to use awaited arguments instead of the latest call's arguments.
-
-
 * `#606 <https://github.com/pytest-dev/pytest-mock/pull/606>`_: ``mocker.resetall(return_value=True, side_effect=True)`` now also applies to non-callable mocks, such as those returned by ``mocker.create_autospec(SomeClass, instance=True)``. Previously both arguments were silently ignored for them.
 * `#547 <https://github.com/pytest-dev/pytest-mock/issues/547>`_: Added ``SpyType`` for annotating ``mocker.spy`` results.
 * Dropped support for EOL Python 3.9.

src/pytest_mock/plugin.py

@@ -204,6 +204,12 @@ 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

@@ -679,6 +679,27 @@ 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]:
     """