started Annex.Sim

Have most of the sim command handler, but to keep it pure while implementing
the rest will need some refactoring.

It seems likely that running the simulation itself will not be able to be
entirely pure. Preferred content evaluation runs in Annex after all.

Note that the somewhat awkward randomWords is because the i386ancient
build depends on a version of random too old to support generating a
random ByteString on its own.

Backend/Hash.hs

@@ -9,13 +9,14 @@
 
 module Backend.Hash (
 	backends,
-	testKeyBackend,
 	keyHash,
 	descChecksum,
 	Hash(..),
 	cryptographicallySecure,
 	hashFile,
-	checkKeyChecksum
+	checkKeyChecksum,
+	testKeyBackend,
+	genTestKey,
 ) where
 
 import Annex.Common
@@ -296,13 +297,25 @@ descChecksum = "checksum"
  -}
 testKeyBackend :: Backend
 testKeyBackend = 
-	let b = genBackendE (SHA2Hash (HashSize 256))
+	let b = genBackendE testKeyHash
 	    gk = case genKey b of
 		Nothing -> Nothing
 		Just f -> Just (\ks p -> addTestE <$> f ks p)
 	in b { genKey = gk }
+
+addTestE :: Key -> Key
+addTestE k = alterKey k $ \d -> d
+	{ keyName = keyName d <> longext
+	}
   where
-	addTestE k = alterKey k $ \d -> d
-		{ keyName = keyName d <> longext
-		}
 	longext = ".this-is-a-test-key"
+
+testKeyHash :: Hash
+testKeyHash = SHA2Hash (HashSize 256)
+
+genTestKey :: L.ByteString -> Key
+genTestKey content = addTestE $ mkKey $ \kd -> kd
+	{ keyName = S.toShort $ encodeBS $
+		(fst $ hasher testKeyHash) content
+	, keyVariety = backendVariety testKeyBackend
+	}