Offset: add tests for hidden elements + scroll

- Also add comments to hidden/disconnected tests noting
  this is to ensure consistency between branches

Author: timmywil

test/data/offset/scroll.html

@@ -11,6 +11,7 @@
 				#scroll-1-1 { top: 1px; left: 1px; }
 					#scroll-1-1-1 { top: 1px; left: 1px; }
 			#forceScroll { width: 5000px; height: 5000px; }
+			#hidden { display: none; }
 			#marker { position: absolute; border: 2px solid #000; width: 50px; height: 50px; background: #ccc; }
 		</style>
 		<script src="../../jquery.js"></script>
@@ -32,6 +33,7 @@
 				<div id="scroll-1-1-1" class="scroll"></div>
 			</div>
 		</div>
+		<div id="hidden"></div>
 		<div id="forceScroll"></div>
 		<div id="marker"></div>
 		<p class="instructions">Click the white box to move the marker to it.</p>

test/unit/offset.js

@@ -52,6 +52,9 @@ test("disconnected element", function() {
 
 	var result = jQuery( document.createElement( "div" ) ).offset();
 
+	// These tests are solely for master/compat consistency
+	// Retrieving offset on disconnected/hidden elements is not officially
+	// valid input, but will return zeros for back-compat
 	equal( result.top, 0, "Retrieving offset on disconnected elements returns zeros (gh-2310)" );
 	equal( result.left, 0, "Retrieving offset on disconnected elements returns zeros (gh-2310)" );
 });
@@ -64,6 +67,9 @@ test("hidden (display: none) element", function() {
 
 	node.remove();
 
+	// These tests are solely for master/compat consistency
+	// Retrieving offset on disconnected/hidden elements is not officially
+	// valid input, but will return zeros for back-compat
 	equal( result.top, 0, "Retrieving offset on hidden elements returns zeros (gh-2310)" );
 	equal( result.left, 0, "Retrieving offset on hidden elements returns zeros (gh-2310)" );
 });
@@ -401,14 +407,20 @@ testIframe("offset/table", "table", function( $ ) {
 });
 
 testIframe("offset/scroll", "scroll", function( $, win ) {
-	expect(28);
+	expect( 30 );
 
 	equal( $("#scroll-1").offset().top, 7, "jQuery('#scroll-1').offset().top" );
 	equal( $("#scroll-1").offset().left, 7, "jQuery('#scroll-1').offset().left" );
 
 	equal( $("#scroll-1-1").offset().top, 11, "jQuery('#scroll-1-1').offset().top" );
 	equal( $("#scroll-1-1").offset().left, 11, "jQuery('#scroll-1-1').offset().left" );
 
+	// These tests are solely for master/compat consistency
+	// Retrieving offset on disconnected/hidden elements is not officially
+	// valid input, but will return zeros for back-compat
+	equal( $("#hidden").offset().top, 0, "Hidden elements do not subtract scroll" );
+	equal( $("#hidden").offset().left, 0, "Hidden elements do not subtract scroll" );
+
 	// scroll offset tests .scrollTop/Left
 	equal( $("#scroll-1").scrollTop(), 5, "jQuery('#scroll-1').scrollTop()" );
 	equal( $("#scroll-1").scrollLeft(), 5, "jQuery('#scroll-1').scrollLeft()" );