iOS / Swift - Unit test for verifying text field limit not exceeded

UITextFieldTestingTests.swift

func testTextFieldLimit() {
    // Set up view before interacting with the text field
    let storyboard = UIStoryboard(name: "Main", bundle: NSBundle(forClass: self.dynamicType))
    let vc = storyboard.instantiateViewControllerWithIdentifier("ViewController") as! ViewController
    vc.loadView()
        
    // Test maximum number of allowable characters
    let atTheLimitString = String(count: maxNumCharacters, repeatedValue: Character("a"))
    let atTheLimitResult = vc.textField(vc.textField, shouldChangeCharactersInRange: NSRange(location: 0, length: 0), replacementString: atTheLimitString)
    XCTAssertTrue(atTheLimitResult, "The text field should allow \(maxNumCharacters) characters")
        
    // Test one more than the maximum number of allowable characters
    let overTheLimitString = String(count: maxNumCharacters+1, repeatedValue: Character("a"))
    let overTheLimitResult = vc.textField(vc.textField, shouldChangeCharactersInRange: NSRange(location: 0, length: 0), replacementString: overTheLimitString)
    XCTAssertFalse(overTheLimitResult, "The text field should not allow \(maxNumCharacters+1) characters")
}