From 2be7b1b6fa88fa2f17ce7d85185580a91d295e2d Mon Sep 17 00:00:00 2001
From: jyviko <2501648+jyviko@users.noreply.github.com>
Date: Fri, 30 Oct 2026 06:38:11 -0400
Subject: [PATCH] Tests: the extruded ellipse is checked by its area, not its
 face count

free_form_profiles_extrude_exactly asked for an ellipse extrusion of exactly
3 faces and a spline-and-line extrusion of at most 5: how many pieces the
kernel cuts a closed side into. It now checks that the sides are exact.

Ellipse a = 10, b = 4, extruded 5: area = 2 pi a b + 5 P, P = 4a E(e),
e^2 = 1 - b^2/a^2. By the Gauss-Kummer series, P = pi (a + b) sum_k
(binom(1/2, k))^2 h^k, h = ((a - b)/(a + b))^2 = 9/49: P = 46.026225191330
(a 200000-point midpoint integral of sqrt(a^2 sin^2 + b^2 cos^2) agrees to
1e-13). A = 80 pi + 230.131126 = 481.458538 mm^2, asserted to 1e-4; a faceted
side would be short of it. Only the top and bottom are planes
(face_types.plane = 2, merged pieces counted once).

The fit spline closed by a line: the planes are its top, bottom and the line's
side (face_types.plane = 3); its volume stays checked against the profile
area.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 crates/engine/src/cmd/sketch_modify_tests.rs | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/crates/engine/src/cmd/sketch_modify_tests.rs b/crates/engine/src/cmd/sketch_modify_tests.rs
index f9e1578bee..08ef485ebe 100644
--- a/crates/engine/src/cmd/sketch_modify_tests.rs
+++ b/crates/engine/src/cmd/sketch_modify_tests.rs
@@ -1259,8 +1259,12 @@ fn free_form_profiles_extrude_exactly() {
     run(&mut s, "solid.extrude", json!({"distance": 5}));
     let v = vol(&mut s);
     assert!((v - pi * 40.0 * 5.0).abs() / (pi * 200.0) < 2e-4, "{v}");
+    // An exact ellipse: its side's area is h times the perimeter, 4a E(e), e² = 1 − b²/a²
+    // (by the Gauss–Kummer series, P = 46.026225), and only the top and bottom are planes.
     let m = run(&mut s, "inspect.measure", json!({}));
-    assert_eq!(m["bodies"][0]["faces"], 3, "an exact ellipse: top, bottom and one side ({m})");
+    let area = m["bodies"][0]["area_mm2"].as_f64().unwrap_or(f64::NAN);
+    assert!((area - (2.0 * pi * 40.0 + 5.0 * 46.026_225_191_329_7)).abs() < 1e-4, "{area} ({m})");
+    assert_eq!(m["bodies"][0]["face_types"]["plane"], 2, "{m}");
     // A region closed by a fit spline and a line.
     let mut s = new_sketch();
     let sp = ids(&run(&mut s, "sketch.spline.fit_point", json!({"points": [[0, 0], [10, 8], [20, 0]]}))["curves"])[0].clone();
@@ -1270,8 +1274,9 @@ fn free_form_profiles_extrude_exactly() {
     run(&mut s, "solid.extrude", json!({"distance": 2}));
     let v = vol(&mut s);
     assert!((v - a * 2.0).abs() / (a * 2.0) < 2e-4, "{v} vs {}", a * 2.0);
+    // Exact: the spline's side is curved, the planes are the top, the bottom and the line's side.
     let m = run(&mut s, "inspect.measure", json!({}));
-    assert!(m["bodies"][0]["faces"].as_u64().unwrap() <= 5, "{m}");
+    assert_eq!(m["bodies"][0]["face_types"]["plane"], 3, "{m}");
 }
 
 #[test]