Factor out common code and test

The findInterimTiles method was used in three renderers.  This change makes it available on the tile source and adds some basic tests.

test/spec/ol/source/tilesource.test.js

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+goog.provide('ol.test.source.TileSource');
+
+describe('ol.source.TileSource', function() {
+
+  describe('constructor', function() {
+    it('returns a tile source', function() {
+      var source = new ol.source.TileSource({
+        projection: ol.Projection.getFromCode('EPSG:4326')
+      });
+      expect(source).toBeA(ol.source.Source);
+      expect(source).toBeA(ol.source.TileSource);
+    });
+  });
+
+  describe('#findLoadedTiles()', function() {
+
+    it('adds no tiles if none are already loaded', function() {
+      // a source with no loaded tiles
+      var source = new ol.test.source.MockTileSource({});
+
+      var loadedTilesByZ = {};
+      var grid = source.getTileGrid();
+      var range = grid.getTileRangeForExtentAndZ(source.getExtent(), 3);
+      source.findLoadedTiles(loadedTilesByZ, 3, range);
+
+      var keys = goog.object.getKeys(loadedTilesByZ);
+      expect(keys.length).toBe(0);
+    });
+
+    it('adds loaded tiles to the lookup (z: 0)', function() {
+      // a source with no loaded tiles
+      var source = new ol.test.source.MockTileSource({
+        '0/0/-1': true,
+        '1/0/-1': true
+      });
+
+      var loadedTilesByZ = {};
+      var grid = source.getTileGrid();
+      var range = grid.getTileRangeForExtentAndZ(source.getExtent(), 0);
+      source.findLoadedTiles(loadedTilesByZ, 0, range);
+      var keys = goog.object.getKeys(loadedTilesByZ);
+      expect(keys.length).toBe(1);
+      var tile = loadedTilesByZ['0']['0/0/-1'];
+      expect(tile).toBeA(ol.Tile);
+      expect(tile.state).toBe(ol.TileState.LOADED);
+    });
+
+    it('adds loaded tiles to the lookup (z: 1)', function() {
+      // a source with no loaded tiles
+      var source = new ol.test.source.MockTileSource({
+        '0/0/-1': true,
+        '1/0/-1': true
+      });
+
+      var loadedTilesByZ = {};
+      var grid = source.getTileGrid();
+      var range = grid.getTileRangeForExtentAndZ(source.getExtent(), 1);
+      source.findLoadedTiles(loadedTilesByZ, 1, range);
+      var keys = goog.object.getKeys(loadedTilesByZ);
+      expect(keys.length).toBe(1);
+      var tile = loadedTilesByZ['1']['1/0/-1'];
+      expect(tile).toBeA(ol.Tile);
+      expect(tile.state).toBe(ol.TileState.LOADED);
+    });
+
+  });
+
+});
+
+/**
+ * Tile source for tests that uses a EPSG:4326 based grid with 4 resolutions and
+ * 256x256 tiles.
+ *
+ * @constructor
+ * @extends {ol.source.TileSource}
+ * @param {Object.<string, boolean>} loaded Lookup of already loaded tiles.
+ */
+ol.test.source.MockTileSource = function(loaded) {
+  var extent = new ol.Extent(-180, -180, 180, 180);
+  var tileGrid = new ol.tilegrid.TileGrid({
+    resolutions: [360 / 256, 180 / 256, 90 / 256, 45 / 256],
+    extent: extent,
+    origin: new ol.Coordinate(-180, 180),
+    tileSize: new ol.Size(256, 256)
+  });
+
+  goog.base(this, {
+    extent: extent,
+    projection: ol.Projection.getFromCode('EPSG:4326'),
+    tileGrid: tileGrid
+  });
+
+  /**
+   * @type {Object.<string, boolean>}
+   * @private
+   */
+  this.loaded_ = loaded;
+
+};
+goog.inherits(ol.test.source.MockTileSource, ol.source.TileSource);
+
+
+/**
+ * @inheritDoc
+ */
+ol.test.source.MockTileSource.prototype.getTile = function(tileCoord) {
+  var tile = new ol.Tile(tileCoord);
+  var key = tileCoord.toString();
+  if (this.loaded_[key]) {
+    tile.state = ol.TileState.LOADED;
+  }
+  return tile;
+};
+
+
+describe('ol.test.source.MockTileSource', function() {
+
+  describe('constructor', function() {
+    it('creates a tile source', function() {
+      var source = new ol.test.source.MockTileSource({});
+      expect(source).toBeA(ol.source.TileSource);
+      expect(source).toBeA(ol.test.source.MockTileSource);
+    });
+  });
+
+  describe('#getTile()', function() {
+    it('returns a tile with state based on constructor arg', function() {
+      var source = new ol.test.source.MockTileSource({
+        '0/0/0': true,
+        '1/0/-1': true
+      });
+      var tile;
+
+      // check a loaded tile
+      tile = source.getTile(new ol.TileCoord(0, 0, 0));
+      expect(tile).toBeA(ol.Tile);
+      expect(tile.state).toBe(ol.TileState.LOADED);
+
+      // check a tile that is not loaded
+      tile = source.getTile(new ol.TileCoord(1, 0, 0));
+      expect(tile).toBeA(ol.Tile);
+      expect(tile.state).toBe(ol.TileState.IDLE);
+
+      // check another loaded tile
+      tile = source.getTile(new ol.TileCoord(1, 0, -1));
+      expect(tile).toBeA(ol.Tile);
+      expect(tile.state).toBe(ol.TileState.LOADED);
+
+    });
+  });
+
+});
+
+goog.require('goog.object');
+
+goog.require('ol.Coordinate');
+goog.require('ol.Extent');
+goog.require('ol.Projection');
+goog.require('ol.Tile');
+goog.require('ol.TileCoord');
+goog.require('ol.TileState');
+goog.require('ol.source.TileSource');
+goog.require('ol.tilegrid.TileGrid');