Initial public release

backend/tests/test_detection_result_pagination.py

@@ -0,0 +1,86 @@
+"""Loading a run's results must not depend on the run being small.
+
+``/detection/runs/{id}/detections`` and its GeoJSON sibling returned every
+persisted detection. A regional run holds tens of thousands, so the endpoints
+the map and the results table call after every run grew without bound. The
+counts stay complete; what is transferred does not.
+"""
+
+from __future__ import annotations
+
+import uuid
+
+import pytest
+
+from app.services.detection_service import DetectionService
+
+
+class _Detection:
+    def __init__(self, index: int) -> None:
+        self.id = uuid.uuid4()
+        self.index = index
+
+
+def _rows(count: int) -> list[_Detection]:
+    return [_Detection(index) for index in range(count)]
+
+
+def test_a_page_is_returned_with_the_complete_total() -> None:
+    page, total, truncated = DetectionService.paginate(_rows(1_000), limit=100, offset=0)
+
+    assert len(page) == 100
+    assert total == 1_000
+    assert truncated is True
+
+
+def test_the_offset_walks_the_population() -> None:
+    page, total, _ = DetectionService.paginate(_rows(10), limit=3, offset=6)
+
+    assert [row.index for row in page] == [6, 7, 8]
+    assert total == 10
+
+
+def test_an_offset_past_the_end_yields_an_empty_page_not_an_error() -> None:
+    page, total, truncated = DetectionService.paginate(_rows(5), limit=10, offset=50)
+
+    assert page == []
+    assert total == 5
+    assert truncated is True
+
+
+def test_a_population_inside_one_page_is_not_reported_as_truncated() -> None:
+    page, total, truncated = DetectionService.paginate(_rows(7), limit=100, offset=0)
+
+    assert len(page) == 7
+    assert total == 7
+    assert truncated is False
+
+
+def test_a_zero_limit_returns_everything_for_callers_that_need_it() -> None:
+    page, total, truncated = DetectionService.paginate(_rows(2_500), limit=0, offset=0)
+
+    assert len(page) == 2_500
+    assert total == 2_500
+    assert truncated is False
+
+
+def test_a_negative_offset_is_treated_as_the_start() -> None:
+    page, _, _ = DetectionService.paginate(_rows(4), limit=2, offset=-5)
+
+    assert [row.index for row in page] == [0, 1]
+
+
+@pytest.mark.parametrize("limit", [1, 2, 3])
+def test_paging_covers_the_population_exactly_once(limit: int) -> None:
+    rows = _rows(7)
+    seen: list[int] = []
+    offset = 0
+    while True:
+        page, total, _ = DetectionService.paginate(rows, limit=limit, offset=offset)
+        if not page:
+            break
+        seen.extend(row.index for row in page)
+        offset += limit
+
+    assert seen == list(range(7))
+    assert total == 7