fails:StringIO#readline when passed [separator] and [limit] raises an IOError if self is at the end
fails:StringIO#readline when passed [separator] and [limit] when passed [separator] and [limit] returns the data read until the limit is consumed or the separator is met
fails:StringIO#readline when passed [separator] and [limit] when passed [separator] and [limit] truncates the multi-character separator at the end to meet the limit
fails:StringIO#readline when passed [separator] and [limit] when passed [separator] and [limit] sets $_ to the read content
fails:StringIO#readline when passed [separator] and [limit] when passed [separator] and [limit] updates self's lineno by one
fails:StringIO#readline when passed [separator] and [limit] when passed [separator] and [limit] tries to convert the passed separator to a String using #to_str
fails:StringIO#readline when passed [separator] and [limit] when passed [separator] and [limit] does not raise TypeError if passed separator is nil
fails:StringIO#readline when passed [separator] and [limit] when passed [separator] and [limit] tries to convert the passed limit to an Integer using #to_int
