A ToDoItem can also have a due date represented by a timestamp. Add the following test to make sure we can initialize an instance of ToDoItem with timestamp:

func test_Init_SetsTimestamp() { 
  let item = ToDoItem(title: "", 
                      timestamp: 0.0) 

  XCTAssertEqual(item.timestamp, 0.0, 
                 "should set timestamp") 
} 

Again, this test does not compile because there is an extra argument in the initializer. From the implementation of the other properties, we know that we have to add a timestamp property in ToDoItem and set it in the initializer:

struct ToDoItem { 
  let title: String 
  let itemDescription: String? 
  let timestamp: Double? 
  
 
  init(title: String, 
       itemDescription: String? = nil, 
       timestamp: Double? = nil) { 
   
  
    self.title = title 
    self.itemDescription = itemDescription 
    self.timestamp = timestamp 
  } 
} 

Run the tests. All the tests pass. The tests are green and there is nothing to refactor.