feat(tests): update test_api.py, add test_interpolate_normalized.py

Author: peng.li24

tests/test_api.py

@@ -414,6 +414,37 @@ def test_values(self, cpp, line, dist):
         assert x == py_pt.x; assert y == py_pt.y
 
 
+class TestLineStringInterpolateNormalized:
+    """Verify interpolate_ls(ls, t, normalized=True) matches Python."""
+    LINE = [(0,0),(10,0),(10,10)]  # L-shaped
+    LINE_CURVED = [(0,0),(3,4),(6,0),(9,4),(12,0)]  # curved path
+
+    @pytest.mark.parametrize("line,t", [
+        (LINE, 0.0), (LINE, 0.25), (LINE, 0.5), (LINE, 0.75), (LINE, 1.0),
+        (LINE_CURVED, 0.0), (LINE_CURVED, 0.2), (LINE_CURVED, 0.5),
+        (LINE_CURVED, 0.8), (LINE_CURVED, 1.0),
+    ])
+    def test_values(self, cpp, line, t):
+        x, y = cpp.interpolate_linestring(cpp.linestring(line), t, True)
+        py_pt = PyLineString(line).interpolate(t, normalized=True)
+        assert x == py_pt.x, f"x: {x} != {py_pt.x}"
+        assert y == py_pt.y, f"y: {y} != {py_pt.y}"
+
+    def test_random_lines(self, cpp):
+        """Random lines with exact comparison."""
+        np.random.seed(42)
+        for _ in range(100):
+            n = np.random.randint(2, 10)
+            pts = np.random.randn(n, 2) * 50
+            pts[:, 0] += np.arange(n) * 10
+            line = pts.tolist()
+            for t in np.linspace(0, 1, 11):
+                x, y = cpp.interpolate_linestring(cpp.linestring(line), float(t), True)
+                py_pt = PyLineString(line).interpolate(float(t), normalized=True)
+                assert x == py_pt.x, f"random line: x {x} != {py_pt.x} at t={t}"
+                assert y == py_pt.y, f"random line: y {y} != {py_pt.y} at t={t}"
+
+
 # =============================================================================
 # Polygon accessors + same-type distance
 # =============================================================================

tests/test_interpolate_normalized.py

@@ -0,0 +1,32 @@
+"""Test: shapelycpp interpolate_ls(normalized=True) vs Python shapely."""
+import sys, os
+sys.path.insert(0, os.path.dirname(__file__))
+
+import numpy as np
+from shapely.geometry import LineString as PyLineString
+from test_api import cpp  # reuse existing test fixture
+
+def test_normalized_random():
+    """100 random lines, 11 normalized positions each."""
+    np.random.seed(42)
+    failures = []
+    for _ in range(100):
+        n = np.random.randint(2, 10)
+        pts = np.random.randn(n, 2) * 50
+        pts[:, 0] += np.arange(n) * 10
+        line = pts.tolist()
+        cpp_ls = cpp.linestring(line)
+        py_ls = PyLineString(line)
+        for i in range(11):
+            t = float(i) / 10.0
+            x, y = cpp.interpolate_linestring(cpp_ls, t, True)
+            py_pt = py_ls.interpolate(t, normalized=True)
+            dx = abs(x - py_pt.x)
+            dy = abs(y - py_pt.y)
+            if dx > 0 or dy > 0:
+                failures.append((line, t, (x, y), (py_pt.x, py_pt.y), dx, dy))
+    assert len(failures) == 0, f"{len(failures)} failures: {failures[:3]}"
+    print(f"PASSED: 100 random lines × 11 positions = 0 mismatch")
+
+if __name__ == "__main__":
+    test_normalized_random()