Add a test case for Future

* Check that future.reason is set to the Exception instance
  when the handler raises Exception (not StandardError)

Author: amutake

spec/concurrent/future_spec.rb

@@ -209,6 +209,11 @@ def trigger_observable(observable)
         expect(future.value).to be_nil
       end
 
+      it 'sets the reason to the Exception instance when the handler raises Exception' do
+        future = Future.new(executor: executor){ raise Exception }.execute
+        expect(future.reason).to be_a(Exception)
+      end
+
       it 'sets the state to :rejected when the handler raises an exception' do
         future = Future.new(executor: executor){ raise StandardError }.execute
         expect(future).to be_rejected