断言有关拖放的错误

Question

当我尝试声明拖放结果（偏移x和y）时，我看到以下错误消息：

我的代码：

var sourceStartLocation = sourceStart.Location;
IWebElement target = driver.FindElement(By.Id("droppablerevert"));
Actions builder = new Actions(driver);
string classBefore = target.GetAttribute("class");

builder.DragAndDrop(sourceStart, target).Perform();

IWebElement fullTarget = driver.FindElement(By.Id("droppablerevert"));
string classAfter = fullTarget.GetAttribute("class");

driver.Manage().Timeouts().ImplicitWait = TimeSpan.FromSeconds(10);

IWebElement sourceEnd = driver.FindElement(By.Id("draggablerevert"));
var sourceEndLocation = sourceEnd.Location;

Assert.AreNotEqual(classBefore, classAfter);        
Assert.AreEqual(sourceStartLocation, sourceEndLocation);