Add compatibility tests for Subgraph children

Author: jcmosc

Tests/OpenAttributeGraphCompatibilityTests/Graph/SubgraphCompatibilityTests.swift

@@ -76,4 +76,59 @@ struct SubgraphCompatibilityTests {
             #expect(notifiedCount == 0)
         }
     }
+    
+    @Suite(.disabled(if: !compatibilityTestEnabled, "Subgraph children is not implemented"), .graphScope)
+    struct ChildrenTests {
+        
+        @Test
+        func addChild() {
+            let graph = Graph()
+            let subgraph = Subgraph(graph: graph)
+            let child = Subgraph(graph: graph)
+            
+            subgraph.addChild(child)
+            #expect(subgraph.childCount == 1)
+            #expect(subgraph.isAncestor(of: child) == true)
+            
+            #expect(subgraph.child(at: 0, tag: nil) == child)
+            
+            #expect(child.parentCount == 1)
+            #expect(child.parent(at: 0) == subgraph)
+            
+            #expect(1 == 2)
+        }
+        
+        @Test
+        func addChildWithTag() {
+            let graph = Graph()
+            let subgraph = Subgraph(graph: graph)
+            let child = Subgraph(graph: graph)
+            
+            subgraph.addChild(child, tag: 1)
+            #expect(subgraph.childCount == 1)
+            #expect(subgraph.isAncestor(of: child) == true)
+            
+            var tag = 0
+            #expect(subgraph.child(at: 0, tag: &tag) == child)
+            #expect(tag == 1)
+            
+            #expect(child.parentCount == 1)
+            #expect(child.parent(at: 0) == subgraph)
+        }
+        
+        @Test
+        func removeChild() {
+            let graph = Graph()
+            let subgraph = Subgraph(graph: graph)
+            let child = Subgraph(graph: graph)
+            
+            subgraph.addChild(child)
+            subgraph.removeChild(child)
+            #expect(subgraph.childCount == 0)
+            #expect(subgraph.isAncestor(of: child) == false)
+            
+            #expect(child.parentCount == 0)
+        }
+        
+    }
 }