Page GRB references for operator samples

backend/tests/test_sprint131_operator_sample_expansion.py

@@ -123,6 +123,81 @@ def test_background_candidate_can_write_empty_reference_geojson(tmp_path: Path,
     assert '"sample_role": "background_candidate"' in payload
 
 
+def test_fetch_reference_follows_grb_next_links_until_complete(tmp_path: Path, monkeypatch) -> None:
+    module = load_sample_preparer()
+    requested: list[tuple[str, dict | None]] = []
+
+    def feature(feature_id: str) -> dict:
+        return {
+            "type": "Feature",
+            "id": feature_id,
+            "geometry": {"type": "Polygon", "coordinates": []},
+            "properties": {},
+        }
+
+    class FeatureResponse:
+        def __init__(self, payload: dict) -> None:
+            self.payload = payload
+
+        def raise_for_status(self) -> None:
+            return None
+
+        def json(self) -> dict:
+            return self.payload
+
+    class FakeRequests:
+        Request = module.requests.Request if module.requests else object
+
+        @staticmethod
+        def get(url, params=None, timeout=120):
+            requested.append((url, params))
+            if len(requested) == 1:
+                return FeatureResponse(
+                    {
+                        "type": "FeatureCollection",
+                        "features": [feature("GBG.1")],
+                        "numberReturned": 1,
+                        "links": [
+                            {
+                                "rel": "next",
+                                "type": "application/geo+json",
+                                "href": "https://example.test/grb?page=2",
+                            }
+                        ],
+                    }
+                )
+            return FeatureResponse(
+                {
+                    "type": "FeatureCollection",
+                    "features": [feature("GBG.2")],
+                    "numberReturned": 1,
+                    "links": [],
+                }
+            )
+
+    monkeypatch.setattr(module, "requests", FakeRequests)
+    monkeypatch.setattr(module, "prepared_url", lambda url, params: f"{url}?prepared=true")
+
+    sample = module.OperatorSample(
+        slug="urban",
+        display_name="Urban",
+        center_lon=5.0,
+        center_lat=51.0,
+    )
+
+    source_url, feature_count = module.fetch_reference(sample, tmp_path / "urban.geojson", [4.9, 50.9, 5.1, 51.1])
+    payload = (tmp_path / "urban.geojson").read_text(encoding="utf-8")
+
+    assert source_url.endswith("?prepared=true")
+    assert feature_count == 2
+    assert requested == [
+        (module.GRB_GBG_URL, {"f": "application/geo+json", "limit": "1000", "bbox": "4.90000000,50.90000000,5.10000000,51.10000000"}),
+        ("https://example.test/grb?page=2", None),
+    ]
+    assert '"id": "GBG.1"' in payload
+    assert '"id": "GBG.2"' in payload
+
+
 def test_reference_sample_still_rejects_empty_grb_response(tmp_path: Path, monkeypatch) -> None:
     module = load_sample_preparer()