Test - Empty Beneficiaries on Withdraw

[gnumonik]

Description

The tests generated in this PR result from modifying the Happy path test generator such that a single (arbitrarily chosen) withdrawal transaction in the generated Tx sequence is submitted with an empty list in the redeemer, yet is otherwise valid.

The relevant functions used to implement these tests are located in Generators.hs:

-- modifies a random element then removes the subsequent elements, 
-- used to ensure the cause of the error is in the modified withdrawal configuration object 
overRandomElemCut :: (a -> a) -> [a] -> Gen [a]
overRandomElemCut f as = do
  i <- chooseInt (0,length as - 1)
  let a  = as !! i
      a' = f a
  pure . take (i+1) $ set (ix i) a' as

overRandomWithdrawConfigCut :: (WithdrawConfig -> WithdrawConfig) -> TestConfig -> Gen TestConfig
overRandomWithdrawConfigCut f (d,ws) = overRandomElemCut f ws >>= \ws' -> pure (d,ws')

emptySignersInWithdrawals :: TestConfig -> Gen TestConfig
emptySignersInWithdrawals = overRandomWithdrawConfigCut $ \w -> w {signers = []}

As expected, each generated Tx sequence fails with a New Beneficiaries are empty error.

These tests support our hypothesis that funds cannot be locked forever at the script address by submitting a transaction with a redeemer containing an empty list of PubKeyHashs.

Conclusion

The above hypothesis proves to hold - therefore no vulnerability was found.