Feature: add export package with StreamingManifestWriter and _dumps

src/documents/tests/export/test_sinks.py

@@ -0,0 +1,29 @@
+import io
+import json
+
+from documents.export.sinks import StreamingManifestWriter
+from documents.export.sinks import _dumps
+
+
+class TestDumps:
+    def test_dumps_is_indented_unicode_json(self) -> None:
+        result: str = _dumps({"a": "é", "b": 1})
+        assert '"é"' in result  # ensure_ascii=False keeps unicode literal
+        assert "\n" in result  # indent=2 produces newlines
+        assert json.loads(result) == {"a": "é", "b": 1}
+
+
+class TestStreamingManifestWriter:
+    def test_writes_json_array_of_records(self) -> None:
+        handle: io.StringIO = io.StringIO()
+        writer: StreamingManifestWriter = StreamingManifestWriter(handle)
+        writer.write_batch([{"pk": 1}, {"pk": 2}])
+        writer.write_record({"pk": 3})
+        writer.close()
+        assert json.loads(handle.getvalue()) == [{"pk": 1}, {"pk": 2}, {"pk": 3}]
+
+    def test_empty_manifest_is_valid_empty_array(self) -> None:
+        handle: io.StringIO = io.StringIO()
+        writer: StreamingManifestWriter = StreamingManifestWriter(handle)
+        writer.close()
+        assert json.loads(handle.getvalue()) == []