README.markdown

Hash ordering test

This test passes on my system right now. (It might not on your system, but that's not important. Change the assert_equal so that it does.)

Now uncomment the @other_hash declaration. It (probably) fails.

That makes the hashing algorithm in Ruby dependent upon the code that runs before it. Which, when you accidentally depend upon the order of keys in a hash, makes for a lot of confusion later on when it no longer works!

The particular example involved verifying that a model accepted nested attributes. We were doing something along the lines of:

model = Factory.build(:model,
  :nested_model => nil, # override the default factory association
  :nested_model_attributes => Factory.attributes_for(:nested_model)
)

That worked when it was first coded. But when we introduced another completely unrelated test in a completely different shoulda context, it broke. To much head-scratching last night!

hash_key_order_test.rb

require 'test/unit'

class HashTest < Test::Unit::TestCase
  def setup
    # @other_hash = {
    #   :h => "something else"
    # }
    @test_hash = {
      :a => "something",
      :b => "something",
      :c => "something",
      :d => "something",
      :e => "something",
      :f => "something",
      :g => "something",
    }
  end

  def test_hash_order
    assert_equal [ :d, :g, :b, :f, :a, :e, :c], @test_hash.keys
  end
end