Add supervisor with backoff restarts

test/Main.hs

@@ -1,12 +1,16 @@
 module Main (main) where
 
 import Test.Hspec (hspec)
+import qualified BackoffProp
 import qualified BusSpec
 import qualified ConnectionSpec
 import qualified RuntimeSpec
+import qualified SupervisorSpec
 
 main :: IO ()
 main = hspec $ do
   BusSpec.spec
   ConnectionSpec.spec
   RuntimeSpec.spec
+  SupervisorSpec.spec
+  BackoffProp.spec