Test that joining a patterned lobed disc is not refused (#1029) (#1051)

Adds a regression test: joining a patterned lobed disc whose copies each share the whole disc with the target is not refused for contact work (#1029).

crates/engine/src/tests.rs

@@ -252,6 +252,28 @@ fn join_of_two_overlapping_rings_is_not_refused() {
     assert!(rel(got, want) < 1e-3, "{got} vs {want}");
 }
 
+/// A disc with a lobe on its rim, patterned six times about its centre: every copy shares the
+/// whole disc with the target, and joining them was refused as too much contact work (#1029).
+#[test]
+fn join_of_a_lobed_disc_pattern_is_not_refused() {
+    let mut s = Session::default();
+    run(&mut s, "sketch.create", json!({"plane": "XY"}));
+    run(&mut s, "sketch.circle.center", json!({"center": [0, 0], "diameter": 15}));
+    run(&mut s, "sketch.circle.center", json!({"center": [0, 7.5], "diameter": 5}));
+    run(&mut s, "sketch.finish", json!({}));
+    run(&mut s, "solid.extrude", json!({"distance": 10, "profiles": "all", "operation": "new", "body_name": "Disc"}));
+    run(&mut s, "solid.pattern.circular", json!({"bodies": ["Disc"], "axis": "Z", "count": 6}));
+    let tools: Vec<String> = s.model.state().bodies.iter().map(|b| b.name.clone()).filter(|n| n != "Disc").collect();
+    assert_eq!(tools.len(), 5);
+    run(&mut s, "solid.combine", json!({"target": "Disc", "tools": tools, "operation": "join"}));
+    assert_eq!(s.model.state().bodies.len(), 1);
+    // The disc plus six lobes, each less the part inside the disc; neighbouring lobes stay apart.
+    let (disc, lobe) = (7.5, 2.5);
+    let want = (PI * disc * disc + 6.0 * (PI * lobe * lobe - disc_overlap(disc, lobe, disc))) * 10.0;
+    let got = volume(&mut s);
+    assert!(rel(got, want) < 1e-3, "{got} vs {want}");
+}
+
 mod boolean_diagnostics;
 mod component_frames;
 mod large_step_import;