quick naive is_substring implementation

gistfile1.rb

def is_substring?(s1, s2)
  match = false
  if s2.length > s1.length
    s1_chars, s2_chars = s1.split(''), s2.split('')
    possible_matches = []
    s2_chars.each_with_index do |c, i|       
      possible_matches << [c, i] if c == s1_chars.first
    end
    possible_matches = possible_matches.map {|c,i| s2_chars.slice(i,s1.length).join}
    match = possible_matches.any? {|candidate| candidate == s1 }
  elsif s2 == s1
    match = true
  end
    
  return match
end

is_substring?("teapot", "I'm a little teapot short and stout.") or raise "FAILED"
is_substring?("foo", "foobar") or raise "FAILED"
is_substring?("bar", "foobar") or raise "FAILED"
is_substring?("FizzBuzz", "FizzBuzz") or raise "FAILED"
!is_substring?("BuzzFizz", "FizzBuzz") or raise "FAILED"
!is_substring?("baz", "foobar") or raise "FAILED"
!is_substring?("baz", "zfoobarba") or raise "FAILED"

puts "PASSED"