Added Tile tests to check for exceptions.

Author: kristiancalhoun

Specs/Scene/TileSpec.js

@@ -0,0 +1,50 @@
+defineSuite([
+         'Scene/Tile',
+         'Core/Math'
+     ], function(
+         Tile,
+         CesiumMath) {
+    "use strict";
+    /*global document,it,expect*/
+
+
+    it("throws without a description", function() {
+        expect(function() {
+            return new Tile();
+        }).toThrow();
+    });
+
+    it("throws without description.extent", function() {
+        expect(function() {
+            return new Tile({
+                x : 0,
+                y : 0
+            });
+        }).toThrow();
+    });
+
+    it("throws without description.zoom", function() {
+        expect(function() {
+            return new Tile({
+                extent : {
+                    north : CesiumMath.PI_OVER_FOUR,
+                    south : 0.0,
+                    east : CesiumMath.PI_OVER_FOUR,
+                    west : -CesiumMath.PI_OVER_FOUR
+                },
+                x : 0,
+                y : 0
+            });
+        }).toThrow();
+    });
+
+    it("throws with negative x or y properties", function() {
+        expect(function() {
+            return new Tile({
+                x : -1.0,
+                y : -1.0,
+                zoom : 1.0
+            });
+        }).toThrow();
+    });
+});