public override string ToString()
{
var result = "----------TO-DO----------\n";
Todos
.ForEach(item =>
result = string.Concat(result,
$"Category: {item.Category.ToString()}, " +
$"Description: {item.Description}.\n"));
result = string.Concat(result, "----------DO-NE----------\n");
Dones
.ForEach(item =>
result = string.Concat(result,
$"Category: {item.Category.ToString()}, " +
$"Description: {item.Description}.\n"));
return(result);
}