Don't cover querying or supplying credits to non-union tables in QLS

We cover the trivial case of querying or supplying credits to tables
that are not derived from a union operation in the unit tests, so we do
not need to spend coverage space in the QLS tests on the trivial cases.

So only gnerate RemainingUnionDebt, SupplyUnionCredits for tables that
are derived from union operations.

Author: dcoutts

test/Test/Database/LSMTree/StateMachine.hs

@@ -1969,42 +1969,36 @@ arbitraryActionWithVars _ label ctx (ModelState st _stats) =
         , let genErrors = pure Nothing -- TODO: generate errors
         ]
      ++ [ (2,  fmap Some $ (Action <$> genErrors <*>) $
-            RemainingUnionDebt <$> genUnionTableVar)
-        | let genErrors = pure Nothing -- TODO: generate errors
+            RemainingUnionDebt <$> genUnionDescendantTableVar)
+            -- Tables not derived from unions are covered in UnitTests.
+        | not (null unionDescendantTableVars)
+        , let genErrors = pure Nothing -- TODO: generate errors
           -- TODO: this is currently only enabled for the reference
           -- implementation. Enable this unconditionally once table union is
           -- implemented
         , isJust (eqT @h @ModelIO.Table)
         ]
      ++ [ (8, fmap Some $ (Action <$> genErrors <*>) $
-            SupplyUnionCredits <$> genUnionTableVar <*> genUnionCredits)
-        | let genErrors = pure Nothing -- TODO: generate errors
+            SupplyUnionCredits <$> genUnionDescendantTableVar <*> genUnionCredits)
+            -- Tables not derived from unions are covered in UnitTests.
+        | not (null unionDescendantTableVars)
+        , let genErrors = pure Nothing -- TODO: generate errors
           -- TODO: this is currently only enabled for the reference
           -- implementation. Enable this unconditionally once table union is
           -- implemented
         , isJust (eqT @h @ModelIO.Table)
         ]
       ++ [ (2, fmap Some $ (Action <$> genErrors <*>) $
-            SupplyPortionOfDebt <$> genUnionTableVar <*> genPortion)
-        | let genErrors  = pure Nothing -- TODO: generate errors
+            SupplyPortionOfDebt <$> genUnionDescendantTableVar <*> genPortion)
+            -- Tables not derived from unions are covered in UnitTests.
+        | not (null unionDescendantTableVars)
+        , let genErrors  = pure Nothing -- TODO: generate errors
           -- TODO: this is currently only enabled for the reference
           -- implementation. Enable this unconditionally once table union is
           -- implemented
         , isJust (eqT @h @ModelIO.Table)
         ]
       where
-        -- For querying the union debt or supplying union credits, the
-        -- interesting cases to test for are when tables are union tables. For
-        -- non-union tables, these operations should just be no-ops, so we
-        -- generate them only rarely.
-        --
-        -- TODO: tweak distribution once table unions are implemented
-        -- TODO: replace union actions on non-union tables with unit tests?
-        genUnionTableVar = QC.frequency [
-            (9 * length unionDescendantTableVars,    genUnionDescendantTableVar)
-          , (1 * length notUnionDescendantTableVars, genNotUnionDescendantTableVar)
-          ]
-
         -- TODO: tweak distribution once table unions are implemented
         genUnionCredits = QC.frequency [
             -- The typical, interesting case is to supply a positive number of