Testing for TheRubyGame Palindrome

palindrome.rb

#!/usr/bin/env ruby

class Palindrome
    return string if string.length == 1
    l = ""
    string.size.times do |i|
      break if string.size - i <= l.size
      c = -1
      while (a = string.rindex(string[i], c)) != i || a - i > l.size do
        b = string[i..a]
        l = b if b == b.reverse && b.size > l.size
        c = a - 1
      end
    end
    l
  end
end

test_palindrome.rb

#!/usr/bin/env ruby

require_relative "palindrome"
require "test/unit"
require "benchmark"

class TestKeygen < Test::Unit::TestCase
  def setup
    @string = "abacdfgdcabaypqqpy"
    @long_string = "abacdfgdcabaypqqpyabacdgfdcasjdkfljaioskdke"
    @superlong_string = "ybd" * 33 + @string
  end

  def test_single_letter_palindrome
    assert_equal "a", Palindrome.find_longest_palindrome("a")
  end

  def test_find_longest_palindrome
    assert_equal "ypqqpy", Palindrome.find_longest_palindrome(@string)
  end

  def test_find_longest_palindrome_reverse
    assert_equal "ypqqpy", Palindrome.find_longest_palindrome(@string.reverse)
  end

  def test_find_longest_palindrome_long
    assert_equal s = @string + @string.reverse, Palindrome.find_longest_palindrome(s)
  end

  def test_find_longest_palindrome_longer
    assert_equal "acdfgdcabaypqqpyabacdgfdca", Palindrome.find_longest_palindrome(@long_string)
  end

  def test_find_longest_palindrome_shorter
    assert_equal "ypqqpy", Palindrome.find_longest_palindrome(@string.reverse + "y")
  end

  def test_find_longest_palindrome_shorter_reverse
    assert_equal "ypqqpy", Palindrome.find_longest_palindrome((@string.reverse + "y").reverse)
  end

  def test_find_longest_palindrome_superlong
    assert_equal "ypqqpy", Palindrome.find_longest_palindrome(@superlong_string)
  end
end