## Advanced

It is typical to call [#to_enum](http://ruby-doc.org/core-2.3.1/Object.html#method-i-to_enum) when defining methods for a generic Enumerable, in case no block is passed.

Here is an additional test you could add:

```ruby
def test_accumulate_when_block_is_deferred
  skip
  accumulate_enumerator = [1, 2, 3].accumulate
  accumulated_result = accumulate_enumerator.each do |number|
    number * number
  end
  assert_equal [1, 4, 9], accumulated_result
end
```