When using the attribute DeploymenItem the newtonsoft could not be found. For example the test below could not be executed unless the Newtonsoft.Json.dll is in the GAC: [CodedUITest] [DeploymentItem(@"Inventory\WebUiTestData.xml", "Inventory")] public class TelerikVSUnitTest1 : BaseTest If it commented out the test will work fine. [TestClass] public class TelerikVSUnitTest1 : BaseTest Details shared internally.