Assert that ol.layer.Tile#getPreload is always set

src/ol/layer/tilelayer.js

@@ -30,18 +30,21 @@ ol.layer.TileProperty = {
 ol.layer.Tile = function(opt_options) {
   var options = goog.isDef(opt_options) ? opt_options : {};
   goog.base(this,  /** @type {olx.layer.LayerOptions} */ (options));
+
+  if (!goog.isDef(this.getPreload())) {
+    this.setPreload(0);
+  }
 };
 goog.inherits(ol.layer.Tile, ol.layer.Layer);
 
 
 /**
- * @return {number|undefined} The level to preload tiles up to.
+ * @return {number} The level to preload tiles up to.
  * @observable
  * @api
  */
 ol.layer.Tile.prototype.getPreload = function() {
-  return /** @type {number|undefined} */ (
+  return /** @type {number} */ (this.get(ol.layer.TileProperty.PRELOAD));
-      this.get(ol.layer.TileProperty.PRELOAD));
 };
 goog.exportProperty(
     ol.layer.Tile.prototype,

src/ol/renderer/layerrenderer.js

@@ -246,8 +246,7 @@ ol.renderer.Layer.prototype.snapCenterToPixel =
  * @param {ol.proj.Projection} projection Projection.
  * @param {ol.Extent} extent Extent.
  * @param {number} currentZ Current Z.
- * @param {number|undefined} preload Load low resolution tiles up to 'preload'
+ * @param {number} preload Load low resolution tiles up to 'preload' levels.
- *     levels.
  * @param {function(this: T, ol.Tile)=} opt_tileCallback Tile callback.
  * @param {T=} opt_this Object to use as `this` in `opt_tileCallback`.
  * @protected
@@ -264,9 +263,6 @@ ol.renderer.Layer.prototype.manageTilePyramid = function(
   var tileQueue = frameState.tileQueue;
   var minZoom = tileGrid.getMinZoom();
   var tile, tileRange, tileResolution, x, y, z;
-  if (!goog.isDef(preload)) {
-    preload = 0;
-  }
   for (z = currentZ; z >= minZoom; --z) {
     tileRange = tileGrid.getTileRangeForExtentAndZ(extent, z, tileRange);
     tileResolution = tileGrid.getResolution(z);

test/spec/ol/layer/tilelayer.test.js

@@ -0,0 +1,33 @@
+goog.provide('ol.test.layer.Tile');
+
+describe('ol.layer.Tile', function() {
+
+  describe('constructor (defaults)', function() {
+
+    var layer;
+
+    beforeEach(function() {
+      layer = new ol.layer.Tile({
+        source: new ol.source.OSM()
+      });
+    });
+
+    afterEach(function() {
+      goog.dispose(layer);
+    });
+
+    it('creates an instance', function() {
+      expect(layer).to.be.a(ol.layer.Tile);
+    });
+
+    it('provides default preload', function() {
+      expect(layer.getPreload()).to.be(0);
+    });
+
+  });
+
+});
+
+goog.require('goog.dispose');
+goog.require('ol.layer.Tile');
+goog.require('ol.source.OSM');