Ruby syntax checker

syntax_checker.rb

require "test/unit"

def syntax_checker(str)
  opening_tags  = ['[', '(', '<', '{']
  closing_tags  = [']', ')', '>', '}']
  
  set = []
  str.chars.each do |char|
    if opening_tags.include?(char)
      set << char
    elsif closing_tags.include?(char)
      if closing_tags.index(char) == opening_tags.index(set.last)
        set.pop 
      else 
        return false 
      end
    end
  end 
  
  set.empty? 
end 


class TestSyntax < Test::Unit::TestCase
  def test_sytax_checker
    assert_equal(true, syntax_checker('<ali> <veli>'))
    assert_equal(true, syntax_checker('<{<[([({ test })])]>}>'))
    assert_equal(true, syntax_checker('( 2 + 1) + (4 + 1)'))
    
    assert_equal(false, syntax_checker('<{<[([({ test ))])]>}>'))
    assert_equal(false, syntax_checker('<div '))
  end
end

usage:

syntax_checker('<ali> <veli>') => true 
syntax_checker('<div ') => false