Verify persistence of SlotInternalIndex values.

Verify that values of type `SlotInternalIndex` can be successfully
written to and read from the database without loss of information.

lib/core/test/unit/Cardano/Wallet/DB/Sqlite/TypesSpec.hs

@@ -14,7 +14,7 @@ import Prelude
 import Cardano.Wallet.DB.Sqlite.Types
     ()
 import Cardano.Wallet.Primitive.Types
-    ( EpochNo (..), SlotId (..), SlotNo (..) )
+    ( EpochNo (..), SlotId (..), SlotInternalIndex (..), SlotNo (..) )
 import Data.Proxy
     ( Proxy (..) )
 import Data.Typeable
@@ -38,6 +38,7 @@ spec :: Spec
 spec = do
     describe "Values can be persisted and unpersisted successfully" $ do
         persistRoundtrip $ Proxy @SlotId
+        persistRoundtrip $ Proxy @SlotInternalIndex
 
 -- | Constructs a test to check that roundtrip persistence and unpersistence is
 --   possible for values of the given type.
@@ -60,6 +61,10 @@ instance Arbitrary SlotId where
     arbitrary = applyArbitrary2 SlotId
     shrink (SlotId en sn) = uncurry SlotId <$> shrink (en, sn)
 
+instance Arbitrary SlotInternalIndex where
+    arbitrary = SlotInternalIndex <$> arbitrary
+    shrink = fmap SlotInternalIndex . shrink . unSlotInternalIndex
+
 instance Arbitrary EpochNo where
     arbitrary = EpochNo <$> arbitrary
     shrink (EpochNo n) = EpochNo <$> shrink n