Add specs for IndirectImmediateExecutor characteristics

Author: obrok

spec/concurrent/executor/indirect_immediate_executor_spec.rb

@@ -8,5 +8,19 @@ module Concurrent
     subject { IndirectImmediateExecutor.new }
 
     it_should_behave_like :executor_service
+
+    it "runs its tasks synchronously" do
+      start = Time.now
+      subject.post { sleep 0.1 }
+
+      expect(Time.now - start).to be >= 0.1
+    end
+
+    it "runs the task on a separate thread" do
+      used_thread = nil
+      subject.post { used_thread = Thread.current }
+
+      expect(used_thread).not_to be(Thread.current)
+    end
   end
 end