ADD explicit error expectations for CollectCom

TODO: need to be explicit with the other mutations also
NOTE: note clear what the MutateHeadTransition is trying to exercise

hydra-node/test/Hydra/Chain/Direct/Contract/CollectCom.hs

@@ -167,7 +167,10 @@ data CollectComMutation
   | -- | Test that collectCom cannot collect from an initial UTxO.
     MutateCommitToInitial
   | MutateHeadTransition
-  | -- | Test that every party has a chance to commit.
+  | -- | Every party should have commited and taken into account for the collectCom transaction to be valid
+    --   Here we increase the number of parties in input and output but keep the commits unchanged. This
+    --   simulate the situation where one participant would not have commited already or whose commit would
+    --   have been ignored by the collectCom transaction.
     MutateNumberOfParties
   | MutateHeadId
   | MutateRequiredSigner
@@ -178,7 +181,7 @@ data CollectComMutation
 genCollectComMutation :: (Tx, UTxO) -> Gen SomeMutation
 genCollectComMutation (tx, _utxo) =
   oneof
-    [ SomeMutation Nothing MutateOpenUTxOHash . ChangeOutput 0 <$> mutateUTxOHash
+    [ SomeMutation (Just "incorrect utxo hash") MutateOpenUTxOHash . ChangeOutput 0 <$> mutateUTxOHash
     , SomeMutation Nothing MutateHeadTransition <$> do
         changeRedeemer <- ChangeHeadRedeemer <$> (Head.Close <$> arbitrary)
         differencCurrencySymbol <- arbitrary `suchThat` (/= toPlutusCurrencySymbol testPolicyId)
@@ -191,7 +194,7 @@ genCollectComMutation (tx, _utxo) =
                     <*> pure differencCurrencySymbol
                 )
         pure $ Changes [changeRedeemer, changeDatum]
-    , SomeMutation Nothing MutateNumberOfParties <$> do
+    , SomeMutation (Just "changed parameters") MutateNumberOfParties <$> do
         -- NOTE: This also mutates the contestation period becuase we could not
         -- be bothered to decode/lookup the current one.
         c <- arbitrary
@@ -201,17 +204,20 @@ genCollectComMutation (tx, _utxo) =
             [ ChangeInputHeadDatum $ Head.Initial c moreParties (toPlutusCurrencySymbol testPolicyId)
             , ChangeOutput 0 $ mutatedPartiesHeadTxOut moreParties headTxOut
             ]
-    , SomeMutation Nothing MutateHeadId <$> do
+    , SomeMutation (Just "ST not spent in transaction") MutateHeadId <$> do
         illedHeadResolvedInput <-
           mkHeadOutput
             <$> pure testNetworkId
             <*> fmap headPolicyId (arbitrary `suchThat` (/= testSeedInput))
             <*> pure (toUTxOContext $ mkTxOutDatum healthyCollectComInitialDatum)
         return $ ChangeInput healthyHeadInput illedHeadResolvedInput (Just $ toScriptData Head.CollectCom)
-    , SomeMutation Nothing MutateRequiredSigner <$> do
+    , SomeMutation (Just "signer is not a participant") MutateRequiredSigner <$> do
         newSigner <- verificationKeyHash <$> genVerificationKey
         pure $ ChangeRequiredSigners [newSigner]
-    , SomeMutation Nothing MutateCommitToInitial <$> do
+    , SomeMutation (Just "datum not found") MutateCommitToInitial <$> do
+        -- we're satisfied with "datum not found" as the current version of the validator will consider
+        -- the initial input as if it were a commit input, hence fetching the datum which is expected
+        -- in a commit and complaining that it did not find it
         (txIn, HealthyCommit{cardanoKey}) <- elements $ Map.toList healthyCommits
         pure $ ChangeInput txIn (toUTxOContext $ mkInitialOutput testNetworkId testPolicyId cardanoKey) Nothing
     , SomeMutation (Just "minting or burning is forbidden") MutateTokenMintingOrBurning

hydra-plutus/src/Hydra/Contract/Head.hs

@@ -182,7 +182,7 @@ checkCollectCom ctx@ScriptContext{scriptContextTxInfo = txInfo} (contestationPer
     && mustNotChangeParameters
     && everyoneHasCommitted
     && mustBeSignedByParticipant ctx headId
-    && hasST headId outValue
+    && traceIfFalse "ST not spent in transaction" (hasST headId outValue)
  where
   mustCollectUtxoHash =
     traceIfFalse "incorrect utxo hash" $