Horspool string matching algorithm in Ruby

alex_horspool.rb

#Horspool algorithm implements the good suffix rule.
# If the char is not present, it still skips ahead by the length of the pattern.
# If the char is not a match, but it is present in the string, it jumps forward by the appropriate ammount.
# pattern_length if char not in pattern is found
# function accepts a string and a pattern and returns the index in the string where
# the pattern first occurs, or "not found"

def brute_search_2 string, pattern
  pattern_length = pattern.length
  bad_match_table = Hash.new

  # Generates hash table with keys as all chars in pattern, and values as the length the last occurence
  # of the char is in the pattern from the end.
  # So for "cake", the table becomes {"c"=>3, "a"=>2, "k"=>1}
  # For "potato", the table becomes {"p"=>5, "o"=>4, "t"=>1, "a"=>2}
  # The table is generated by iterating through the pattern and saving the char at the current index as the
  # key, and setting the value as the pattern_length minus the current index minus 1.

  for i in (0...pattern_length - 1)
    bad_match_table[pattern[i]] = pattern_length - i - 1
  end

  # Iterate through the string starting at string[pattern_length-1]
  # we cant do a for loop, because we need to add pattern_length to string_index
  # when the char is not in our bad_match_table hash
  # therefore we must define string_index as pattern_length -1 and iterate up ourselves
  string_index = pattern_length - 1
  while string_index < string.length
    match_count = 0
    loop do
      # if a non-match is found, then break.
      break if string[string_index - match_count] != pattern[(pattern_length - 1 - match_count)]
      # if it wasn't a non-match, it must be a match!
      match_count += 1
      # if that match_count reaches the lenght of the pattern, you found the pattern!
      # return the index in string where the pattern begins
      return string_index - (pattern_length - 1) if match_count == pattern_length
    end
    if bad_match_table[string[string_index]]
      string_index += bad_match_table[string[string_index]]
    else
      string_index += pattern_length
    end
  end
  return "not found"
end

# tests
puts " "
puts "Brute Force Right to Left Test:"
puts " "

# match
test_string     = "let them eat cake"
test_pattern = "cake"
should_be    = 13
result       = brute_search_2 test_string, test_pattern

puts "Pattern at index #{result} "
raise "This is wrong" unless result == should_be

# no match
test_string2     = "let them eat cake"
test_pattern2 = "potato"
should_be2    = "not found"
result2       = brute_search_2 test_string2, test_pattern2

puts "Pattern at index #{result2} "

raise "This is wrong" unless result == should_be

Alex, thanks for this. Should your code at line 70 be:
raise "This is wrong" unless result2 == should_be2 ?