Add test case for two closed layers

Author: Peter554

rust/src/graph/higher_order_queries.rs

@@ -329,4 +329,57 @@ mod tests {
             ])
         );
     }
+
+    #[test]
+    fn test_generate_module_permutations_two_closed_layers() {
+        let mut graph = Graph::default();
+
+        // Create four layers with the middle two closed
+        let top_module = graph.get_or_add_module("app.top").token;
+        let middle_top_module = graph.get_or_add_module("app.middle-top").token;
+        let middle_bottom_module = graph.get_or_add_module("app.middle-bottom").token;
+        let bottom_module = graph.get_or_add_module("app.bottom").token;
+
+        let mut top_layer = FxHashSet::default();
+        top_layer.insert(top_module);
+
+        let mut middle_top_layer = FxHashSet::default();
+        middle_top_layer.insert(middle_top_module);
+
+        let mut middle_bottom_layer = FxHashSet::default();
+        middle_bottom_layer.insert(middle_bottom_module);
+
+        let mut bottom_layer = FxHashSet::default();
+        bottom_layer.insert(bottom_module);
+
+        let top_level = Level::new(top_layer, false, false);
+        let middle_top_level = Level::new(middle_top_layer, false, true); // Closed
+        let middle_bottom_level = Level::new(middle_bottom_layer, false, true); // Closed
+        let bottom_level = Level::new(bottom_layer, false, false);
+
+        let levels = vec![
+            top_level,
+            middle_top_level,
+            middle_bottom_level,
+            bottom_level,
+        ];
+
+        let permutations = graph.generate_illegal_import_permutations_for_layers(&levels);
+
+        assert_eq!(
+            permutations,
+            FxHashSet::from_iter([
+                (bottom_module, middle_bottom_module),
+                (bottom_module, middle_top_module),
+                (bottom_module, top_module),
+                (middle_bottom_module, middle_top_module),
+                (middle_bottom_module, top_module),
+                (middle_top_module, top_module),
+                // Permutations due to closed middle layers.
+                (top_module, middle_bottom_module),
+                (top_module, bottom_module),
+                (middle_top_module, bottom_module),
+            ])
+        );
+    }
 }