Add tests for KDTree arc-distance queries

.gitignore

@@ -23,6 +23,10 @@ __pycache__
 
 # virtual environment
 venv/
+.venv/
+
+# Editor settings
+.vscode/
 
 # Installer logs
 pip-log.txt

libpysal/cg/tests/test_kdtree.py

@@ -0,0 +1,39 @@
+# Tests derived from Arc_KDTree docstring examples to get the expected behavior
+
+
+import math
+
+import pytest
+
+from libpysal.cg import sphere
+from libpysal.cg.kdtree import KDTree
+
+
+def test_arc_kdtree_basic_query():
+    pts = [(0, 90), (0, 0), (180, 0), (0, -90)]
+    kd = KDTree(pts, distance_metric="Arc", radius=sphere.RADIUS_EARTH_KM)
+
+    d, i = kd.query((90, 0), k=4)
+
+    assert len(d) == 4
+    assert len(i) == 4
+
+
+def test_arc_distance_quarter_circumference():
+    pts = [(0, 90), (0, 0), (180, 0), (0, -90)]
+    kd = KDTree(pts, distance_metric="Arc", radius=sphere.RADIUS_EARTH_KM)
+
+    d, _ = kd.query((90, 0), k=4)
+
+    expected = 2 * math.pi * sphere.RADIUS_EARTH_KM / 4
+    assert abs(d[0] - expected) < 1e-5
+
+
+def test_arc_query_ball_point_raises_for_large_radius():
+    pts = [(0, 0), (90, 0)]
+    kd = KDTree(pts, distance_metric="Arc", radius=sphere.RADIUS_EARTH_KM)
+
+    too_large_radius = kd.circumference
+
+    with pytest.raises(ValueError):
+        kd.query_ball_point((0, 0), r=too_large_radius)