Reject malformed spline counts and unsorted knots

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/tests/test_formula.py b/tests/test_formula.py
index 7440681..10065d2 100644
--- a/tests/test_formula.py
+++ b/tests/test_formula.py
@@ -168,3 +168,29 @@ class SplineTest(unittest.TestCase):
         g.add_prop("b")
         g.add_formula("b", spline_ops("spline_linear", [[0, 0], [1, 10]]))
         self.assertAlmostEqual(g.evaluate()["b"], 5.0)
+
+    def test_fractional_count_is_fatal(self):
+        g = Graph()
+        g.add_prop("a", 0.5)
+        g.add_prop("b")
+        ops = [push("a"), val([0, 0]), val([1, 1]), val(2.5), {"op": "spline_linear"}]
+        g.add_formula("b", ops, source="f")
+        with self.assertRaisesRegex(Error, "malformed formula for b"):
+            g.evaluate()
+
+    def test_unsorted_knots_are_fatal(self):
+        g = Graph()
+        g.add_prop("a", 0.5)
+        g.add_prop("b")
+        g.add_formula("b", spline_ops("spline_linear", [[1, 1], [0, 0], [2, 5]]), source="f")
+        with self.assertRaisesRegex(Error, "malformed formula for b"):
+            g.evaluate()
+
+    def test_count_larger_than_stack_is_fatal(self):
+        g = Graph()
+        g.add_prop("a", 0.5)
+        g.add_prop("b")
+        ops = [push("a"), val(0), val(1), {"op": "spline_linear"}]
+        g.add_formula("b", ops, source="f")
+        with self.assertRaisesRegex(Error, "malformed formula for b"):
+            g.evaluate()