containsOneItem() : The containsOneItem() method returns true if the collection contains exactly one item; otherwise, false is returned.
collect([1]).containsOneItem();
// true
collect({ firstname: 'Luis' }).containsOneItem();
// true
collect('value').containsOneItem();
// true
collect([1, 2, 3]).containsOneItem();
// false
collect({ firstname: 'Luis', lastname: 'Díaz' }).containsOneItem();
// false
collect().containsOneItem();
// false
collect([]).containsOneItem();
// false
collect({}).containsOneItem();
// false
