Incorporating @elemoine's review comments

tests/Layer/Grid.html

@@ -968,7 +968,7 @@
     }
 
     function test_applyBackBuffer(t) {
-        t.plan(9);
+        t.plan(12);
 
         var map = new OpenLayers.Map('map2');
         var layer = new OpenLayers.Layer.WMS('', '', {}, {
@@ -1025,7 +1025,25 @@
         t.eq(layer.backBuffer.style.top, '295px',
              'back buffer has correct top');
 
-        map.destroy();
+         // test #4
+         // and a back buffer in the layer and do as if back buffer removal
+         // has been scheduled, and test that applyBackBuffer removes the
+         // back buffer and clears the timer
+         layer.createBackBuffer = function() {
+             return;
+         };
+         backBuffer = document.createElement('div');
+         map.layerContainerDiv.insertBefore(backBuffer, map.baseLayer.div);
+         layer.backBuffer = backBuffer;
+         layer.backBufferTimerId = 'fake';
+         layer.applyBackBuffer(2);
+         t.ok(backBuffer !== map.layerContainerDiv.firstChild,
+              'back buffer is not first child of layer container div');
+         t.eq(layer.backBuffer, null,
+              'back buffer not set in layer');
+         t.eq(layer.backBufferTimerId, null,
+              'back buffer timer cleared');
+         map.destroy();
     }
 
     function test_createBackBuffer(t) {
@@ -1269,6 +1287,55 @@
         OpenLayers.Tile.Image.prototype.createBackBuffer = origCreateBackBuffer
     }
 
+
+    function test_delayed_back_buffer_removal(t) {
+        //
+        // Test that the delaying of the back buffer removal behaves
+        // as expected.
+        //
+
+        t.plan(5);
+
+        // set up
+        
+        var map = new OpenLayers.Map('map', {
+            resolutions: [32, 16, 8, 4, 2, 1],
+            zoomMethod: null
+        });
+        var layer = new OpenLayers.Layer.WMS('', '', {}, {
+            isBaseLayer: true,
+            transitionEffect: 'resize'
+        });
+        map.addLayer(layer);
+        map.setCenter(new OpenLayers.LonLat(0, 0), 0);
+
+        map.zoomTo(1);
+
+        t.ok(layer.backBuffer === map.layerContainerDiv.firstChild,
+             '[a] back buffer is first child of layer container div');
+
+        // Mark one tile loaded, to see if back buffer removal gets scheduled.
+        layer.grid[1][1].onImageLoad();
+
+        t.ok(layer.backBufferTimerId !== null,
+             '[a] back buffer scheduled for removal');
+
+        var backBuffer = layer.backBuffer;
+
+        map.zoomTo(2);
+
+        t.ok(layer.backBuffer !== backBuffer,
+             '[b] a new back buffer was created');
+        t.ok(layer.backBuffer === map.layerContainerDiv.firstChild,
+             '[b] back buffer is first child of layer container div');
+        t.ok(layer.backBufferTimerId === null,
+             '[b] back buffer no longer scheduled for removal');
+
+        // tear down
+
+        map.destroy();
+    }
+
     function test_getGridData(t) {
         t.plan(12);