Some test for [bug 8210](http://bugs.ruby-lang.org/issues/8210)

gistfile1.rb

# encoding: UTF-8 

# see [s.o. question](http://stackoverflow.com/questions/15779859/does-multibyte-character-interfere-with-end-line-character-within-a-regex)

p RUBY_VERSION
p __ENCODING__ unless RUBY_VERSION.start_with? "1.8"

class String
  def last
    self[-1,1]
  end
end

# TEST 1
s = "んにちは"
p "TEST 1: \"#{s}\" where last character \"#{s.last}\" is #{s.last.bytes.size} bytes"
# TEST 1.1
test_for_zero_or_one_of = "ん"
p "test for zero or one of #{test_for_zero_or_one_of} [#{test_for_zero_or_one_of.bytes.size} bytes]"
n = s =~ /#{test_for_zero_or_one_of}?\z/u
p "s =~ /#{test_for_zero_or_one_of}?\z/u #=> #{n ? n : 'nil'}" 
# TEST 1.2
test_for_zero_or_one_of = "ç"
p "test for zero or one of #{test_for_zero_or_one_of} [#{test_for_zero_or_one_of.bytes.size} bytes]"
n = s =~ /#{test_for_zero_or_one_of}?\z/u
p "s =~ /#{test_for_zero_or_one_of}?\z/u #=> #{n ? n : 'nil' }" 
n = s =~ /x?#{test_for_zero_or_one_of}?\z/u
p "s =~ /x?#{test_for_zero_or_one_of}?\z/u #=> #{n ? n : 'nil'}" 
# TEST 1.3
test_for_zero_or_one_of = "\n"
p "test for zero or one of \n [#{test_for_zero_or_one_of.bytes.size} bytes]"
n = s =~ /#{test_for_zero_or_one_of}?\z/u
n = s =~ /\n?\z/u
p "s =~ /\n?\z/u #=> #{n ? n : 'nil' }" 
n = s =~ /\n?\n?\z/u
p "s =~ /\n?\n?\z/u #=> #{n ? n : 'nil'}" 
n = s =~ /\n?\n?\n?\z/u
p "s =~ /\n?\n?\n?\z/u #=> #{n ? n : 'nil'}" 
p "NB: if the last multi-byte character of the string is 3 bytes , then the 'zero or one before' test only works when we test for at least 3 bytes (not 3 character) before"

######
# TEST 2
s = "in French there is the ç"
s_last_character = "ç"
p "TEST 2: \"#{s}\" where last character \"#{s.last}\" is #{s_last_character.bytes.size} bytes"
# TEST 2.1
test_for_zero_or_one_of = "ん"
p "test for zero or one of #{test_for_zero_or_one_of} [#{test_for_zero_or_one_of.bytes.size} bytes]"
n = s =~ /#{test_for_zero_or_one_of}?\z/u
p "s =~ /#{test_for_zero_or_one_of}?\z/u #=> #{n ? n : 'nil'}" 
# TEST 2.2
test_for_zero_or_one_of = "é"
p "test for zero or one of #{test_for_zero_or_one_of} [#{test_for_zero_or_one_of.bytes.size} bytes]"
n = s =~ /#{test_for_zero_or_one_of}?\z/u
p "s =~ /#{test_for_zero_or_one_of}?\z/u #=> #{n ? n : 'nil' }" 
n = s =~ /x?#{test_for_zero_or_one_of}?\z/u
p "s =~ /x?#{test_for_zero_or_one_of}?\z/u #=> #{n ? n : 'nil'}" 
# TEST 2.3
test_for_zero_or_one_of = "\n"
p "test for zero or one of \n [#{test_for_zero_or_one_of.bytes.size} bytes]"
n = s =~ /#{test_for_zero_or_one_of}?\z/u
n = s =~ /\n?\z/u
p "s =~ /\n?\z/u #=> #{n ? n : 'nil' }" 
n = s =~ /\n?\n?\z/u
p "s =~ /\n?\n?\z/u #=> #{n ? n : 'nil'}" 
n = s =~ /\n?\n?\n?\z/u
p "s =~ /\n?\n?\n?\z/u #=> #{n ? n : 'nil'}" 
p "NB: if the last multi-byte character of the string is 2 bytes , then the 'zero or one before' test only works when we test for at least 2 bytes (not 2 character) before"

######
# TEST 3
p "TEST 3 - When the multi-byte character is not at the end of the string there is no problem"
p "\"ç\" bytes: #{"ç".bytes.to_a.join(",")}"
s = "abçd"
p "string is \"#{s}\""
n = s =~ /x?b/u
p " zero or one x preceding b, match:#{n}"
n = s =~ /x?d/u
p " zero or one x preceding d, match:#{n}"
n = s =~ /x?x?d/u
p " zero or two x preceding d, match:#{n}"
n = s =~ /x?ç/u
p " zero or one x preceding ç, match:#{n}"
n = s =~ /x?x?ç/u
p " zero or two x preceding ç, match:#{n}"