custom_matcher.rb

# This custom matcher can be used to test state machine
#
# Examples
#
#   transition = OpenStruct.new(:name => :operation1, :state_field => :status, :from => :state1, :to => :state2)
#   it { should have_transition(transition) }
#
#   transition = {:name => :operation2, :state_field => :status, :from => :state2, :to => :state3}
#   it { should have_transition(transition) }
RSpec::Matchers.define :have_transition do |transition|
  match do |model|
    transition = OpenStruct(transition)
    events = model.class.state_machines[transition.state_field].events
    event = events[transition.name]

    events.valid_for(model, :from => transition.from, :to => transition.to) == [event]
  end

  def OpenStruct(params)
    params.is_a?(OpenStruct) ? params : OpenStruct.new(params)
  end
end

gearbox.rb

class GearBox
  state_machine :gear, :initial => :P do
    event :switch_to_r do
      transition [:P, :N] => :R
    end

    event :switch_to_n do
      transition [:R, :D] => :N
    end
    
    event :switch_to_d do
      transition :N => :D
    end
    
    event :switch_to_p do
      transition :R => :P
    end
  end
end

gearbox_spec.rb

require 'spec_helper'

describe GearBox do
  context '#gear'
    let(:from_p_to_r) do
      OpenStruct.new({
        :state_field => :gear,
        :name => :switch_to_r,
        :from => :P,
        :to => :R
      })
    end

    let(:from_n_to_r) do
      OpenStruct.new({
        :state_field => :gear,
        :name => :switch_to_r,
        :from => :N,
        :to => :R
      })
    end
    
    let(:from_r_to_n) do
      OpenStruct.new({
        :state_field => :gear,
        :name => :switch_to_n,
        :from => :R,
        :to => :N
      })    
    end

    let(:from_d_to_n) do
      OpenStruct.new({
        :state_field => :gear,
        :name => :switch_to_n,
        :from => :D,
        :to => :N
      })    
    end
    
    let(:from_n_to_d) do
      OpenStruct.new({
        :state_field => :gear,
        :name => :switch_to_d,
        :from => :n,
        :to => :d
      })        
    end
    
    let(:from_r_to_p) do
      OpenStruct.new({
        :state_field => :gear,
        :name => :switch_to_p,
        :from => :R,
        :to => :P
      })        
    end
    
    it { should be_p } # check initial gear
    it { should have_transition from_p_to_r }
    it { should have_transition from_n_to_r }
    it { should have_transition from_r_to_n }
    it { should have_transition from_d_to_n }
    it { should have_transition from_n_to_d }
    it { should have_transition from_r_to_p }
  end
end