Wait for needed UTxO some time

If two RollbackAndForward actions are generated next to each other
then submitTx fails. Waiting for a small amount of time to pass so
that the needed utxo is present fixes this problem.

Ideally the fix would be: Correctly implemented rollbacks in the mock
chain but perhaps this is enough for now.

hydra-node/test/Hydra/Model/MockChain.hs

@@ -127,6 +127,21 @@ mockChainAndNetwork tr seedKeys commits = do
     let vks = getVerificationKey . signingKey . snd <$> seedKeys
     env{participants = verificationKeyToOnChainId <$> vks}
 
+  -- In case of two consecutive rollback actions it can happen that the
+  -- tx can't be evaluated to be correct. Waiting for some time to
+  -- see the needed inputs helps resolve these errors
+  waitToEvaluateTx n chain tx = do
+    (_, _, _, utxo) <- readTVarIO chain
+    let result = evaluateTx tx utxo
+    if n == 0
+       then pure (result, utxo)
+       else
+        case result of
+          Left _ -> threadDelay 0.1 >> waitToEvaluateTx (n - 1) chain tx
+          Right report
+            | any isLeft report -> threadDelay 0.1 >> waitToEvaluateTx (n - 1) chain tx
+            | otherwise -> pure (result, utxo)
+
   connectNode nodes chain queue node = do
     localChainState <- newLocalChainState (initHistory initialChainState)
     let Environment{party = ownParty} = env node
@@ -140,29 +155,30 @@ mockChainAndNetwork tr seedKeys commits = do
             }
     let getTimeHandle = pure $ fixedTimeHandleIndefiniteHorizon `generateWith` 42
     let HydraNode{eq = EventQueue{putEvent}} = node
+
     -- Validate transactions on submission and queue them for inclusion if valid.
-    let submitTx tx =
-          atomically $ do
-            (_, _, _, utxo) <- readTVar chain
-            -- TODO: dry with block tx validation
-            case evaluateTx tx utxo of
-              Left err ->
-                throwSTM . userError . toString $
-                  unlines
-                    [ "MockChain: Invalid tx submitted"
-                    , "Tx: " <> toText (renderTxWithUTxO utxo tx)
-                    , "Error: " <> show err
-                    ]
-              Right report
-                | any isLeft report ->
-                    throwSTM . userError . toString $
-                      unlines
-                        [ "MockChain: Invalid tx submitted"
-                        , "Tx: " <> toText (renderTxWithUTxO utxo tx)
-                        , "Error: " <> show (lefts . toList $ report)
-                        ]
-                | otherwise ->
-                    writeTQueue queue tx
+    let submitTx tx = do
+          (result, utxo) <- waitToEvaluateTx (2 :: Int) chain tx
+          -- TODO: dry with block tx validation
+          case result of
+            Left err ->
+              atomically . throwSTM . userError . toString $
+                unlines
+                  [ "MockChain: Invalid tx submitted"
+                  , "Tx: " <> toText (renderTxWithUTxO utxo tx)
+                  , "Error: " <> show err
+                  ]
+            Right report
+              | any isLeft report ->
+                  atomically . throwSTM . userError . toString $
+                    unlines
+                      [ "MockChain: Invalid tx submitted"
+                      , "Tx: " <> toText (renderTxWithUTxO utxo tx)
+                      , "Error: " <> show (lefts . toList $ report)
+                      ]
+              | otherwise ->
+                  atomically $ writeTQueue queue tx
+
     let chainHandle =
           createMockChain
             tr