Add compatibility tests for tree

Author: jcmosc

Tests/OpenAttributeGraphCompatibilityTests/Graph/SubgraphCompatibilityTests.swift

@@ -128,4 +128,11 @@ struct SubgraphCompatibilityTests {
             #expect(child.parentCount == 0)
         }
     }
+    
+    @Test
+    func treeRoot() {
+        let graph = Graph()
+        let subgraph = Subgraph(graph: graph)
+        let _ = subgraph.treeRoot
+    }
 }

Tests/OpenAttributeGraphCompatibilityTests/Graph/TreeCompatibilityTests.swift

@@ -0,0 +1,61 @@
+//
+//  TreeCompatibilityTests.swift
+//  OpenAttributeGraphCompatibilityTests
+
+import Testing
+
+@MainActor
+@Suite(.graphScope)
+struct TreeCompatibilityTests {
+    
+    @Test
+    func treeElement() {
+        let graph = Graph()
+        let subgraph = Subgraph(graph: graph)
+        
+        let treeElement = subgraph.treeRoot
+        #expect(treeElement == nil)
+        
+        let _ = treeElement?.type
+        let _ = treeElement?.value
+        let _ = treeElement?.flags
+        let _ = treeElement?.parent
+    }
+    
+    @Test
+    func values() {
+        let graph = Graph()
+        let subgraph = Subgraph(graph: graph)
+        
+        let treeElement = subgraph.treeRoot
+        var values = treeElement?.values
+        
+        let treeValue = values?.next()
+        let _ = treeValue?.type
+        let _ = treeValue?.value
+        let _ = treeValue?.key
+        let _ = treeValue?.flags
+    }
+    
+    @Test
+    func nodes() {
+        let graph = Graph()
+        let subgraph = Subgraph(graph: graph)
+        
+        let treeElement = subgraph.treeRoot
+        var nodes = treeElement?.nodes
+        
+        let _ = nodes?.next()
+    }
+    
+    @Test
+    func children() {
+        let graph = Graph()
+        let subgraph = Subgraph(graph: graph)
+        
+        let treeElement = subgraph.treeRoot
+        var children = treeElement?.children
+        
+        let _ = children?.next()
+    }
+}