text: fails:String#lines splits using default newline separator when none is specified
  fails:String#lines splits self using the supplied record separator and passes each substring to the block
  fails:String#lines taints substrings that are passed to the block if self is tainted
  fails:String#lines passes self as a whole to the block if the separator is nil
  fails:String#lines yields paragraphs (broken by 2 or more successive newlines) when passed ''
  fails:String#lines uses $/ as the separator when none is given
  fails:String#lines yields subclass instances for subclasses
  fails:String#lines returns self
  fails:String#lines tries to convert the separator to a string using to_str
  fails:String#lines does not care if the string is modified while substituting
  fails:String#lines raises a TypeError when the separator can't be converted to a string
  fails:String#lines accepts a string separator
  fails:String#lines raises a TypeError when the separator is a symbol
  fails:String#lines returns an enumerator when no block given
  fails:String#lines returns an array when no block given
  