Refactor: extract QuerySetStream, shared by search and LLM indexing (#13431)

src/documents/tests/test_utils.py

@@ -0,0 +1,35 @@
+import pytest_mock
+
+from documents.utils import QuerySetStream
+
+
+class TestQuerySetStream:
+    def test_len_and_iter_delegate_to_streaming_queryset_methods(
+        self,
+        mocker: pytest_mock.MockerFixture,
+    ) -> None:
+        """
+        GIVEN:
+            - A mock queryset
+        WHEN:
+            - A QuerySetStream wrapping it is measured and iterated
+        THEN:
+            - len() uses count() (not a materializing len()), and iteration
+              uses .iterator(chunk_size=...) (not plain iteration, which
+              would materialize the whole queryset, plus any prefetch
+              caches, into Django's own result cache at once)
+        """
+        mock_queryset = mocker.MagicMock()
+        mock_queryset.count.return_value = 42
+        mock_queryset.iterator.return_value = iter(["row-1", "row-2"])
+        streamed = QuerySetStream(mock_queryset, chunk_size=1000)
+
+        assert len(streamed) == 42
+        assert list(streamed) == ["row-1", "row-2"]
+        # count.call_count isn't asserted exactly: list()'s own size-hint
+        # optimization calls len(streamed) again internally, on top of the
+        # explicit len() call above -- both legitimately delegate to
+        # count(), so only the delegation itself (not the call count) is
+        # the thing being verified here.
+        mock_queryset.count.assert_called_with()
+        mock_queryset.iterator.assert_called_once_with(chunk_size=1000)