fails:StringIO#read_nonblock when passed length, buffer truncates buffer when limit is nil and no data reamins
fails:StringIO#read_nonblock when passed length, buffer returns a String in ASCII-8BIT ignoring the encoding of the source String and buffer
fails:StringIO#read_nonblock when passed length returns a String in ASCII-8BIT encoding when passed a length > 0
fails:StringIO#read_nonblock when passed length returns an empty String in ASCII-8BIT encoding when passed length == 0
fails:StringIO#read_nonblock when passed no arguments reads the whole content starting from the current position
fails:StringIO#read_nonblock when passed no arguments updates the current position
fails:StringIO#read_nonblock when passed no arguments returns an empty String when no data remains
fails:StringIO#read_nonblock when passed no arguments returns a String in the same encoding as the source String
fails:StringIO#read_nonblock when passed no arguments returns an empty String in ASCII-8BIT encoding
fails:StringIO#read_nonblock when self is not readable raises an IOError
fails:StringIO#read_nonblock when passed nil returns an empty String in ASCII-8BIT encoding
fails:StringIO#read_nonblock when passed length returns an empty String when passed 0 and no data remains
