Prune all except for the most recent z on URL change

test/spec/ol/tilecache.test.js

@@ -0,0 +1,39 @@
+goog.require('ol.Tile');
+goog.require('ol.TileCache');
+goog.require('ol.tilecoord');
+
+
+describe('ol.TileCache', function() {
+
+  describe('#pruneExceptNewestZ()', function() {
+    it('gets rid of all entries that are not at the newest z', function() {
+      var tiles = [
+        new ol.Tile([0, 0, 0]),
+        new ol.Tile([1, 0, 0]),
+        new ol.Tile([1, 1, 0]),
+        new ol.Tile([2, 0, 0]),
+        new ol.Tile([2, 1, 0]),
+        new ol.Tile([2, 2, 0]),
+        new ol.Tile([2, 3, 0]) // newest tile at z: 2
+      ];
+      var cache = new ol.TileCache();
+
+      sinon.spy(tiles[0], 'dispose');
+
+      tiles.forEach(function(tile) {
+        cache.set(ol.tilecoord.getKey(tile.tileCoord), tile);
+      });
+
+      cache.pruneExceptNewestZ();
+
+      expect(cache.getKeys()).to.eql([
+        '2/3/0',
+        '2/2/0',
+        '2/1/0',
+        '2/0/0'
+      ]);
+
+      expect(tiles[0].dispose.calledOnce).to.be(true);
+    });
+  });
+});