Enable coverage check on main property

Using lower Confidence values, we should not see way very long tests at
the cost of occasional false positives. In such cases, the actual
coverage numbers and "interesting values" test should give an indication
whether it was rightfully failing or would have taken just very long.

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

@@ -77,7 +77,7 @@ import Test.Hydra.Tx.Gen (
   genVerificationKey,
  )
 import Test.Hydra.Tx.Mutation (addParticipationTokens)
-import Test.QuickCheck (Property, Smart (..), Testable, checkCoverage, cover, elements, frequency, ioProperty, shuffle, sublistOf, (===))
+import Test.QuickCheck (Confidence (..), Property, Smart (..), Testable, checkCoverage, checkCoverageWith, cover, elements, frequency, ioProperty, shuffle, sublistOf, (===))
 import Test.QuickCheck.Monadic (monadic)
 import Test.QuickCheck.StateModel (
   ActionWithPolarity (..),
@@ -103,20 +103,26 @@ spec = do
     realWorldModelUTxO (u1 <> u2) === (realWorldModelUTxO u1 <> realWorldModelUTxO u2)
   prop "generates interesting transaction traces" $ \actions ->
     checkCoverage $ coversInterestingActions actions True
-  prop "all valid transactions" prop_runActions
+  prop "all valid transactions" $
+    -- NOTE: Using lower confidence to improve performance. In case of an error,
+    -- check coverage numbers and also the distribution in above test (which is
+    -- way faster).
+    checkCoverageWith
+      Confidence{certainty = 100, tolerance = 0.8}
+      prop_runActions
 
 coversInterestingActions :: Testable p => Actions Model -> p -> Property
 coversInterestingActions (Actions_ _ (Smart _ steps)) p =
   p
     & cover 1 (null steps) "empty"
     & cover 50 (hasSomeSnapshots steps) "has some snapshots"
     & cover 5 (hasDecrement steps) "has decrements"
-    & cover 1 (countContests steps >= 2) "has multiple contests"
+    & cover 0.1 (countContests steps >= 2) "has multiple contests"
     & cover 5 (closeNonInitial steps) "close with non initial snapshots"
     & cover 10 (hasFanout steps) "reach fanout"
-    & cover 0.5 (fanoutWithEmptyUTxO steps) "fanout with empty UTxO"
-    & cover 1 (fanoutWithSomeUTxO steps) "fanout with some UTxO"
-    & cover 0.5 (fanoutWithDelta steps) "fanout with additional UTxO to distribute"
+    & cover 10 (fanoutWithEmptyUTxO steps) "fanout with empty UTxO"
+    & cover 10 (fanoutWithSomeUTxO steps) "fanout with some UTxO"
+    & cover 10 (fanoutWithDelta steps) "fanout with additional UTxO to distribute"
  where
   hasSomeSnapshots =
     any $
@@ -302,8 +308,8 @@ instance StateModel Model where
     case headState of
       Open{} ->
         frequency $
-          [(5, Some . NewSnapshot <$> genSnapshot)]
-            <> [ ( 10
+          [(3, Some . NewSnapshot <$> genSnapshot)]
+            <> [ ( 3
                  , do
                     actor <- elements allActors
                     snapshot <- elements knownSnapshots
@@ -331,7 +337,7 @@ instance StateModel Model where
                     , deltaUTxO = pendingDecommit
                     }
           )
-            : [ ( 3
+            : [ ( 10
                 , do
                     actor <- elements allActors
                     snapshot <- elements knownSnapshots