Update isArray_ function and add test coverage

spec/suites/UtilSpec.js

@@ -20,4 +20,21 @@ describe("jasmine.util", function() {
       expect(destination).toEqual({foo: null});
     });
   });
+
+  describe("isArray_", function() {
+    it("should return true if the argument is an array", function() {
+      expect(jasmine.isArray_([])).toBe(true);
+      expect(jasmine.isArray_(['a'])).toBe(true);
+      expect(jasmine.isArray_(new Array())).toBe(true);
+    });
+
+    it("should return false if the argument is not an array", function() {
+      expect(jasmine.isArray_(undefined)).toBe(false);
+      expect(jasmine.isArray_({})).toBe(false);
+      expect(jasmine.isArray_(function() {})).toBe(false);
+      expect(jasmine.isArray_('foo')).toBe(false);
+      expect(jasmine.isArray_(5)).toBe(false);
+      expect(jasmine.isArray_(null)).toBe(false);
+    });
+  });
 });