You should test the callback methods and its correct invocation in two separate tests. Understand the ActiveRecord note before you move on with this note.

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Say this is your Spaceship class with a transition launch and a release_docking_clamps callback:

class Spaceship
  state_machine :state, :initial => :docked do
    event :launch do
      transition :docked => :en_route
    end
    before_transition :on => :launch, :do => :release_docking_clamps
  end
end

Testing that a state_machine callback is called at the correct point in a record's lifecycle is a little tricky because it isn't a regular callback chain you can invoke with run_callbacks. Besides writing a real record to the database (which you shouldn't do for performance reasons), there are several ways to work around this.

1. Use it_should_receive_callbacks

The awesome it_should_run_callbacks macro from spec_candy has been upgraded to work with state_machine callbacks:

describe Spaceship do

  describe '#launch from :docked to :en_route' do
    it_should_run_callbacks(:release_docking_clamps)
  end

  describe '#release_docking_clamps' do
    # test clamp mechanism here
  end

end

This does not currently distinguish between before_transition and after_transition.

2. Instantiate a state_machine transition

You can obtain the state machine's callback chain and run that. This is what spec_candy wraps for you (method #1).

describe Spaceship do

  describe '#launch' do
    it 'should run the proper callbacks' do
      subject.state = 'docked'
      subject.should_receive :release_docking_clamps
      transition = StateMachine::Transition.new(subject, Spaceship.state_machine, :launch, :docked, :en_route)
      transition.run_callbacks
    end
  end

  describe '#release_docking_clamps' do
    # test clamp mechanism here
  end

end

3. Use keep_invalid!

By using the keep_invalid! helper from spec_candy you can directly invoke the transition and not worry about hitting the database:

describe Spaceship do

  describe '#launch' do
    it 'should run the proper callbacks' do
      subject.state = 'docked'
      subject.should_receive :release_docking_clamps
      subject.keep_invalid!
      subject.launch
    end
  end

  describe '#release_docking_clamps' do
    # test clamp mechanism here
  end

end

This method might not work with after_transition callbacks (please investigate and report back here).