Rails: How to test state_machine?

The question is old, but I had the same one. Taking example from state_machine gem :

class Vehicle
  state_machine :state, :initial => :parked do
    event :park do
      transition [:idling, :first_gear] => :parked
    end

    event :ignite do
      transition :stalled => same, :parked => :idling
    end

    event :idle do
      transition :first_gear => :idling
    end

    event :shift_up do
      transition :idling => :first_gear, :first_gear => :second_gear, :second_gear => :third_gear
    end

    event :shift_down do
      transition :third_gear => :second_gear, :second_gear => :first_gear
    end
  end
end

My solution was:

describe Vehicle do

  before :each do
    @vehicle = Factory(:vehicle)
  end

  describe 'states' do
    describe ':parked' do
      it 'should be an initial state' do
        # Check for @vehicle.parked? to be true
        @vehicle.should be_parked
      end

      it 'should change to :idling on :ignite' do
        @vehicle.ignite!
        @vehicle.should be_idling
      end

      ['shift_up!', 'shift_down!'].each do |action|
        it "should raise an error for #{action}" do
          lambda {@job_offer.send(action)}.should raise_error
        end
      end
    end
  end
end

I was using:

• ruby (1.9.3)
• rails (3.1.3)
• rspec (2.8.0.rc1)
• factory_girl (2.3.2)
• state_machine (1.1.0)

The state_machine_rspec gem includes many helper methods for writing concise specs.

 describe Ratification do
   it { should have_states :boss, :declarant, :done, :owner }
   it { should handle_events :approve, when: :boss }
   it { should handle_events :approve, when: :owner }
   it { should handle_events :divert, when: :boss }
   it { should handle_events :divert, when: :owner }
   it { should handle_events :repeat, when: :declarant }
   it { should reject_events :approve, :divert, :repeat, when: :done }
   it { should reject_events :approve, :divert, :repeat, when: :done }
 end

These RSpec matchers will assist with the state_machine specs from a high-level. From here, one needs to write the specs for the business cases for can_approve?, can_divert?, and can_repeat?.

I have written a RSpec custom matcher. It allows to test state flow in elegant and simple way: check it out

Unfortunately, I think you need to put a test for each state -> state transition, which might feel like code duplication.

describe Ratification do
  it "should initialize to :boss" do
    r = Ratification.new
    r.boss?.should == true
  end

  it "should move from :boss to :owner to :done as it's approved" do
    r = Ratification.new
    r.boss?.should == true
    r.approve
    r.owner?.should == true
    r.approve
    r.done?.should == true
  end

  # ...
end

Fortunately, I think this usually fits into integration testing. For instance, an extremely simple state machine for a payments system would be:

class Bill < ActiveRecord::Base
  belongs_to :account

  attr_protected :status_events

  state_machine :status, :initial => :unpaid do
    state :unpaid
    state :paid

    event :mark_as_paid do
      transition :unpaid => :paid
    end
  end
end

You might still have the unit tests as above, but you'll probably also have integration testing, something like:

describe Account do
  it "should mark the most recent bill as paid" do
    @account.recent_bill.unpaid?.should == true
    @account.process_creditcard(@credit_card)
    @account.recent_bill.paid?.should == true
  end
end

That was a lot of handwaiving, but hopefully that makes sense. I'm also not super used to RSpec, so hopefully I didn't make too many mistakes there. If there's a more elegant way to test this, I haven't found it yet.