feat: add extensible operators and golden flows

tests/test_golden_flows.py

@@ -0,0 +1,55 @@
+from __future__ import annotations
+
+import json
+import unittest
+from pathlib import Path
+
+from govoplan_dataflow.backend.executor import execute_preview
+from govoplan_dataflow.backend.graph import validate_graph
+from govoplan_dataflow.backend.schemas import PipelineGraph
+
+
+FIXTURES = Path(__file__).parents[1] / "fixtures" / "golden"
+
+
+class GoldenFlowTests(unittest.TestCase):
+    def test_every_golden_flow_matches_its_expected_output(self) -> None:
+        directories = sorted(
+            path for path in FIXTURES.iterdir() if path.is_dir()
+        )
+        self.assertGreaterEqual(len(directories), 2)
+        for directory in directories:
+            with self.subTest(flow=directory.name):
+                manifest = _json(directory / "manifest.json")
+                graph_payload = _json(directory / str(manifest["graph"]))
+                for item in graph_payload["nodes"]:
+                    fixture = item.get("config", {}).get("fixture")
+                    if fixture:
+                        item["config"]["rows"] = _json(
+                            directory / "inputs" / fixture
+                        )
+                graph = PipelineGraph.model_validate(graph_payload)
+                diagnostics = validate_graph(graph)
+                self.assertEqual(
+                    [],
+                    [
+                        item.model_dump()
+                        for item in diagnostics
+                        if item.severity == "error"
+                    ],
+                )
+
+                result = execute_preview(graph, row_limit=500)
+
+                self.assertEqual(
+                    _json(directory / str(manifest["expected_output"])),
+                    result.rows,
+                )
+
+
+def _json(path: Path):
+    return json.loads(path.read_text(encoding="utf-8"))
+
+
+if __name__ == "__main__":
+    unittest.main()