public void Complete_SetsTodoItemCompleteFlagToTrue()
{
// arrange
var list = new TodoList();
list.Add(new("Test 1"));
// act
list.Complete(1);
// assert
var completedItem = Assert.Single(list.All);
Assert.NotNull(completedItem);
Assert.Equal(1, completedItem.Id);
Assert.True(completedItem.Complete);
}
