iOS get UI element from XCUIElement

I'm trying to test a custom UITextField element in a UITableView showing error message after a button click. My element has an error icon inside so if I can have my custom UITextField object in test class, I can check if the icon is visible or not. I can get a XCUIElement object by doing:

XCUIApplication().tables.cells.containingType(.StaticText, identifier: "My placeholder").childrenMatchingType(.TextField).element

How can I get a UITextField object inside of a XCTestCase class?