Swift UI Testing Access string in the TextField

Swhift 4.2. You need to clear an existing value in textField and paste new value.

let app = XCUIApplication()
let textField = app.textFields["yourTextFieldValue"]
textField.tap()
textField.clearText(andReplaceWith: "VALUE")
XCTAssertEqual(textField.value as! String, "VALUE", "Text field value is not correct")

where clearText is a method of XCUIElement extension:

extension XCUIElement {
    func clearText(andReplaceWith newText:String? = nil) {
        tap()
        press(forDuration: 1.0)
        var select = XCUIApplication().menuItems["Select All"]

        if !select.exists {
            select = XCUIApplication().menuItems["Select"]
        }
        //For empty fields there will be no "Select All", so we need to check
        if select.waitForExistence(timeout: 0.5), select.exists {
            select.tap()
            typeText(String(XCUIKeyboardKey.delete.rawValue))
        } else {
            tap()
        }
        if let newVal = newText {
            typeText(newVal)
        }
    }
}

I use this code and it works fine:

textField.typeText("value")
XCTAssertEqual(textField.value as! String, "value")

If you're doing something similar and it isn't functioning, I would check to make sure that your textField element actually exists:

XCTAssertTrue(textField.exists, "Text field doesn't exist")
textField.typeText("value")
XCTAssertEqual(textField.value as! String, "value", "Text field value is not correct")