fails:IO#each_codepoint returns an Enumerator when passed no block
fails:IO#each_codepoint yields each codepoint
fails:IO#each_codepoint yields each codepoint starting from the current position
fails:IO#each_codepoint raises an error if reading invalid sequence
fails:IO#each_codepoint does not change $_
fails:IO#each_codepoint raises an IOError when self is not readable
fails:IO#each_codepoint calls the given block
fails:IO#each_codepoint returns self
