Add Test to make sure associated objects live/die with lifetime of UIView.

Summary: Wrote some tests to make sure the associated objects we use for layout live and die with the objects. This was worthwhile because it made me realize UIView+CSSLayout wasn't enabled to ARC. As a result, my tests were failing because they weren't explicitly deallocing nodes.

Reviewed By: rnystrom

Differential Revision: D4023324

fbshipit-source-id: 5356cf4f0522582d75f83b5eb2193d9bc8d63aee

uikit/CSSLayout/Tests/CSSLayoutTests.m

@@ -16,6 +16,36 @@
 
 @implementation CSSLayoutTests
 
+- (void)testNodesAreDeallocedWithSingleView
+{
+  XCTAssertEqual(0, CSSNodeGetInstanceCount());
+
+  UIView *view = [[UIView alloc] initWithFrame:CGRectZero];
+  [view css_setFlex:1];
+  XCTAssertEqual(1, CSSNodeGetInstanceCount());
+  view = nil;
+
+  XCTAssertEqual(0, CSSNodeGetInstanceCount());
+}
+
+- (void)testNodesAreDeallocedCascade
+{
+  XCTAssertEqual(0, CSSNodeGetInstanceCount());
+
+  UIView *view = [[UIView alloc] initWithFrame:CGRectZero];
+  [view css_setFlex:1];
+
+  for (int i=0; i<10; i++) {
+    UIView *subview = [[UIView alloc] initWithFrame:CGRectZero];
+    [subview css_setFlex:1];
+    [view addSubview:subview];
+  }
+  XCTAssertEqual(11, CSSNodeGetInstanceCount());
+  view = nil;
+
+  XCTAssertEqual(0, CSSNodeGetInstanceCount());
+}
+
 - (void)testHiddenViewsAreNotMeasured
 {
   const CGSize firstSize = CGSizeMake(100, 100);