support RSpec matcher allow_transition_to

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ## unreleased
 
- * add RSpec matchers `have_state`, `allow_event` (see [issue #147](https://github.com/aasm/aasm/issues/147) for details)
+ * add RSpec matchers `have_state`, `allow_event` and `allow_transition_to` (see [issue #147](https://github.com/aasm/aasm/issues/147) for details)
  * add RSpec matcher `transition_from` (see [issue #178](https://github.com/aasm/aasm/issues/178) for details, thanks to [@thomasstephane](https://github.com/thomasstephane))
 
 ## 4.4.1

README.md

@@ -723,7 +723,7 @@ Job.aasm.states_for_select
 
 ### Testing
 
-AASM provides some matchers for [RSpec](http://rspec.info): `transition_from`, `have_state`. Add `require 'aasm/rspec'` to your `spec_helper.rb` file and use them like this
+AASM provides some matchers for [RSpec](http://rspec.info): `transition_from`, `have_state`, `allow_event` and `allow_transition_to`. Add `require 'aasm/rspec'` to your `spec_helper.rb` file and use them like this
 
 ```ruby
 # classes with only the default state machine
@@ -734,6 +734,8 @@ expect(job).to have_state(:sleeping)
 expect(job).not_to have_state(:running)
 expect(job).to allow_event :run
 expect(job).to_not allow_event :clean
+expect(job).to allow_transition_to(:running)
+expect(job).to_not allow_transition_to(:cleaning)
 
 # classes with multiple state machine
 multiple = SimpleMultipleExample.new
@@ -743,12 +745,16 @@ expect(multiple).to have_state(:standing).on(:move)
 expect(multiple).not_to have_state(:walking).on(:move)
 expect(multiple).to allow_event(:walk).on(:move)
 expect(multiple).to_not allow_event(:hold).on(:move)
+expect(multiple).to allow_transition_to(:walking).on(:move)
+expect(multiple).to_not allow_transition_to(:running).on(:move)
 expect(multiple).to transition_from(:sleeping).to(:processing).on_event(:start).on(:work)
 expect(multiple).to_not transition_from(:sleeping).to(:sleeping).on_event(:start).on(:work)
 expect(multiple).to have_state(:sleeping).on(:work)
 expect(multiple).not_to have_state(:processing).on(:work)
 expect(multiple).to allow_event(:start).on(:move)
 expect(multiple).to_not allow_event(:stop).on(:move)
+expect(multiple).to allow_transition_to(:processing).on(:move)
+expect(multiple).to_not allow_transition_to(:sleeping).on(:move)
 ```
 
 ## <a id="installation">Installation ##

lib/aasm/rspec/allow_transition_to.rb

@@ -0,0 +1,22 @@
+RSpec::Matchers.define :allow_transition_to do |state|
+  match do |obj|
+    @state_machine_name ||= :default
+    obj.aasm(@state_machine_name).states(:permitted => true).include?(state)
+  end
+
+  chain :on do |state_machine_name|
+    @state_machine_name = state_machine_name
+  end
+
+  description do
+    "allow transition to #{expected} (on :#{@state_machine_name})"
+  end
+
+  failure_message do |obj|
+    "expected that the state :#{expected} would be reachable (on :#{@state_machine_name})"
+  end
+
+  failure_message_when_negated do |obj|
+    "expected that the state :#{expected} would not be reachable (on :#{@state_machine_name})"
+  end
+end

spec/unit/rspec_matcher_spec.rb

@@ -19,6 +19,21 @@ describe 'state machine' do
     end
   end
 
+  describe 'allow_transition_to' do
+    it "works for simple state machines" do
+      expect(simple).to allow_transition_to(:filled_out)
+      expect(simple).to_not allow_transition_to(:authorised)
+    end
+
+    it "works for multiple state machines" do
+      expect(multiple).to allow_transition_to(:walking).on(:move)
+      expect(multiple).to_not allow_transition_to(:standing).on(:move)
+
+      expect(multiple).to allow_transition_to(:processing).on(:work)
+      expect(multiple).to_not allow_transition_to(:sleeping).on(:work)
+    end
+  end
+
   describe "have_state" do
     it "works for simple state machines" do
       expect(simple).to have_state :initialised