This example should not fail with rspec, but...

rspec_should_change_bug.rb

require 'rubygems'
require 'rspec'

class TestBug
  attr_reader :array
  
  def initialize
    @array = []
  end
  
  def add(n)
    @array << n
  end
end

describe TestBug do
  it "should NOT fail" do
    @bug = TestBug.new
    
    expect {
      @bug.add(1)
    }.to change {
      @bug.array
    }.from([]).to([1])
  end
end