[ButtonBar] Update tests to reflect that titleTextAttributes appearan…

…ce only works on iOS 9.

Summary: Part of https://github.com/google/material-components-ios/issues/370.

Reviewers: #mdc_ios_owners, junius, iangordon

Reviewed By: #mdc_ios_owners, junius, iangordon

Subscribers: iangordon

Projects: #material_components_ios

Differential Revision: http://codereview.cc/D685

components/ButtonBar/tests/unit/ButtonBarIssue370Tests.swift

@@ -18,7 +18,7 @@ import XCTest
 import MaterialComponents
 
 // Tests confirming that the Button Bar respects UI appearance for bar button item
-// titleTextAttributes.
+// titleTextAttributes on iOS 9 and above.
 //
 // Based on issue https://github.com/google/material-components-ios/issues/370
 class ButtonBarIssue370Tests: XCTestCase {
@@ -49,6 +49,12 @@ class ButtonBarIssue370Tests: XCTestCase {
 
   func testGlobalAppearanceOnly() {
     UIBarButtonItem.appearance().setTitleTextAttributes(globalAttributes, forState: .Normal)
+
+    if UIBarButtonItem.appearance().titleTextAttributesForState(.Normal) == nil {
+      // This feature is not supported on this OS
+      return
+    }
+
     let item = UIBarButtonItem(title: "Text", style: .Plain, target: nil, action: nil)
     buttonBar.items = [item]
 
@@ -76,6 +82,12 @@ class ButtonBarIssue370Tests: XCTestCase {
 
   func testGlobalAppearanceAndDirectMerging() {
     UIBarButtonItem.appearance().setTitleTextAttributes(fontAttributes, forState: .Normal)
+
+    if UIBarButtonItem.appearance().titleTextAttributesForState(.Normal) == nil {
+      // This feature is not supported on this OS
+      return
+    }
+
     let item = UIBarButtonItem(title: "Text", style: .Plain, target: nil, action: nil)
     item.setTitleTextAttributes(directAttributes, forState: .Normal)
     buttonBar.items = [item]