Speed up the recently added "database is busy" SQLite3 test

It was passing but only after ~57 seconds because the busy_timeout setting in
the test definition was being applied to a different connection than was being
used by the implementation.

With this change we hook into the connection function and apply the shorter
busy_timeout after the normal setup work is done but before handing the
connection off to application code.

test/Persistence.hs

@@ -205,16 +205,24 @@ sqlite3DatabaseVoucherPaymentTests =
     sqlite3Tests =
       testGroup "SQLite3-specific voucher"
       [ testCase "database is busy" $ do
-          getDB <- makeDatabase
-          db <- getDB
-          case db of
+          aDatabase <- makeDatabase
+          normalConnection <- aDatabase
+          case normalConnection of
             (SQLiteDB connect) -> do
+              -- Acquire a write lock before letting the application code run
+              -- so that the application code is denied the write lock.
+              normalConn <- connect
+              fastBusyConn <- fastBusyConnection connect
+              Sqlite.withExclusiveTransaction normalConn $ do
+                result <- redeemVoucher fastBusyConn voucher fingerprint
+                assertEqual "Redeeming voucher while database busy" result $ Left DatabaseUnavailable
+      ]
+      where
+        fastBusyConnection
+          :: IO Sqlite.Connection
+          -> IO VoucherDatabaseState
+        fastBusyConnection connect = do
           conn <- connect
           -- Tweak the timeout down so the test completes quickly
           Sqlite.execute_ conn "PRAGMA busy_timeout = 0"
-              -- Acquire a write lock before letting the application code run so that
-              -- the application code is denied the write lock.
-              Sqlite.withExclusiveTransaction conn $ do
-                result <- redeemVoucher db voucher fingerprint
-                assertEqual "Redeeming voucher while database busy" result $ Left DatabaseUnavailable
-      ]
+          return . SQLiteDB . return $ conn