fails:Enumerator::Lazy#flat_map returns a new instance of Enumerator::Lazy
fails:Enumerator::Lazy#flat_map sets nil to size
fails:Enumerator::Lazy#flat_map calls the block with initial values when yield with multiple arguments
fails:Enumerator::Lazy#flat_map raises an ArgumentError when not given a block
fails:Enumerator::Lazy#flat_map when the returned lazy enumerator is evaluated by Enumerable#first stops after specified times
fails:Enumerator::Lazy#flat_map when the returned lazy enumerator is evaluated by Enumerable#first flattens elements when the given block returned an array or responding to .each and .force
fails:Enumerator::Lazy#flat_map on a nested Lazy sets nil to size
fails:Enumerator::Lazy#flat_map on a nested Lazy when the returned lazy enumerator is evaluated by Enumerable#first stops after specified times
fails:Enumerator::Lazy#flat_map on a nested Lazy when the returned lazy enumerator is evaluated by Enumerable#first flattens elements when the given block returned an array or responding to .each and .force
