TxSpec: No need for property tests and suchThat

We generate perfect ModelSnapshot anyway and then alter it (or alter the
UTxO) to get expected failures so we don't depend on anything arbitrary
here.

hydra-node/test/Hydra/Chain/Direct/TxSpec.hs

@@ -83,7 +83,7 @@ import Hydra.Contract.HeadState qualified as HeadState
 import Hydra.Contract.HeadTokens (headPolicyId, mkHeadTokenScript)
 import Hydra.Contract.Initial qualified as Initial
 import Hydra.Crypto (aggregate, sign)
-import Hydra.Data.ContestationPeriod (addContestationPeriod, contestationPeriodFromDiffTime)
+import Hydra.Data.ContestationPeriod (contestationPeriodFromDiffTime)
 import Hydra.HeadId (HeadId (..))
 import Hydra.Ledger (hashUTxO)
 import Hydra.Ledger.Cardano (adaOnly, addInputs, addReferenceInputs, addVkInputs, emptyTxBody, genOneUTxOFor, genTxOutWithReferenceScript, genUTxO1, genUTxOAdaOnlyOfSize, genValue, genVerificationKey, unsafeBuildTransaction)
@@ -108,7 +108,6 @@ import Test.QuickCheck (
   forAllBlind,
   label,
   property,
-  suchThat,
   vectorOf,
   withMaxSuccess,
   (.&&.),
@@ -258,7 +257,7 @@ spec =
                   ]
 
     describe "Decrement" $ do
-      prop "Alter snapshots to trigger validator errors" $
+      it "Alter snapshots to trigger validator errors" $
         forAllBlind arbitrary $ \chainContext -> do
           let ctx@ChainContext{scriptRegistry} =
                 chainContext{ownVerificationKey = alicePVk, networkId = testNetworkId}
@@ -497,11 +496,10 @@ evaluateAndMatchError tx spendableUTxO expectedError =
 
 genPerfectModelSnapshot :: Gen ModelSnapshot
 genPerfectModelSnapshot = do
-  snapshotNumber <- arbitrary
   (decommit, amount) <- arbitrary
   let decommitUTxO = Map.fromList [(decommit, amount)]
-  snapshotUTxO <- arbitrary `suchThat` (\a -> all (> amount) (Map.elems a) && (decommit `elem` Map.keys a))
-  pure $ ModelSnapshot{snapshotNumber, snapshotUTxO, decommitUTxO}
+  snapshotUTxO' <- arbitrary
+  pure $ ModelSnapshot{snapshotNumber = 1, snapshotUTxO = Map.union snapshotUTxO' decommitUTxO, decommitUTxO}
 
 -- | Check auxiliary data of a transaction against 'pparams' and whether the aux
 -- data hash is consistent.