Issue #263: adds a coverage test for UTxO

byron/ledger/executable-spec/test/Ledger/UTxO/Properties.hs

@@ -93,6 +93,8 @@ relevantCasesAreCovered = withTests 400 $ property $ do
 
     cover 20 "avg. nr. of tx outputs (1,5]" (1 <= avgOutputs && avgOutputs <= 5)
     cover 20 "avg. nr. of tx outputs (5,10]" (5 < avgOutputs && avgOutputs <= 10)
+
+    cover 80 "starting UTxO has no future outputs" (all (== empty) (futureOutputs tr))
   where
     -- | The average "fee surplus" for transactions in the trace.
     --   Could be zero if all the transactions had zero surplus fee.
@@ -116,6 +118,16 @@ relevantCasesAreCovered = withTests 400 $ property $ do
           fee = unLovelace $ balance (txins tx_ ◁ utxo_) - balance (txouts tx_)
           minFee = unLovelace $ txMinFee tx_
 
+    -- | The intersection of the starting UTxO and each transaction in
+    -- a trace
+    futureOutputs :: Trace UTXOW -> [Set TxIn]
+    futureOutputs tr =
+      let
+        UTxOState {utxo = utxo0} = _traceInitState tr
+        txs = body <$> traceSignals OldestFirst tr
+      in
+        (\ti -> dom (txouts ti) ∩ dom utxo0) <$> txs
+
 -- | Returns the average number of inputs and outputs for a list of transactions.
 avgInputsOutputs :: [Tx] -> (Double, Double)
 avgInputsOutputs txs