Support insertion on first layout of display node

AsyncDisplayKitTests/ASDisplayNodeImplicitHierarchyTests.m

@@ -0,0 +1,66 @@
+//
+//  ASDisplayNodeImplicitHierarchyTests.m
+//  AsyncDisplayKit
+//
+//  Created by Levi McCallum on 2/1/16.
+//  Copyright © 2016 Facebook. All rights reserved.
+//
+
+#import <XCTest/XCTest.h>
+
+#import "ASDisplayNode.h"
+#import "ASDisplayNode+Beta.h"
+#import "ASDisplayNode+Subclasses.h"
+#import "ASStaticLayoutSpec.h"
+
+@interface ASSpecTestDisplayNode : ASDisplayNode
+
+@property (copy, nonatomic) ASLayoutSpec * (^layoutSpecBlock)(ASSizeRange constrainedSize);
+
+@end
+
+@implementation ASSpecTestDisplayNode
+
+- (ASLayoutSpec *)layoutSpecThatFits:(ASSizeRange)constrainedSize
+{
+  return self.layoutSpecBlock(constrainedSize);
+}
+
+@end
+
+@interface ASDisplayNodeImplicitHierarchyTests : XCTestCase
+
+@end
+
+@implementation ASDisplayNodeImplicitHierarchyTests
+
+- (void)setUp {
+  [super setUp];
+  [ASDisplayNode setUsesImplicitHierarchyManagement:YES];
+}
+
+- (void)tearDown {
+  [ASDisplayNode setUsesImplicitHierarchyManagement:NO];
+  [super tearDown];
+}
+
+- (void)testFeatureFlag
+{
+  XCTAssert([ASDisplayNode usesImplicitHierarchyManagement]);
+}
+
+- (void)testInitialNodeInsertion
+{
+  ASDisplayNode *node1 = [[ASDisplayNode alloc] init];
+  ASDisplayNode *node2 = [[ASDisplayNode alloc] init];
+  ASSpecTestDisplayNode *node = [[ASSpecTestDisplayNode alloc] init];
+  node.layoutSpecBlock = ^(ASSizeRange constrainedSize){
+    return [ASStaticLayoutSpec staticLayoutSpecWithChildren:@[node1, node2]];
+  };
+  [node measureWithSizeRange:ASSizeRangeMake(CGSizeZero, CGSizeZero)];
+  [node layout]; // Layout immediately
+  XCTAssertEqual(node.subnodes[0], node1);
+  XCTAssertEqual(node.subnodes[1], node2);
+}
+
+@end