How come to_s doesn't work here?

####################################
require 'test/unit'
class TOY_CASE<Test::Unit::TestCase

def test_toy_test

aoa = [[1,2,3],[4,5,6]]

aoa.each do |arr|
	arr.each do |item|
		item = item.to_s
		end
		assert_equal(["1","2","3"],arr)
end


end #def
end #class
##########################################