submitMustFail

-- SubmitMustFail.daml
module SubmitMustFail where

import Daml.Script

template Vault
  with
    owner   : Party
    balance : Decimal
  where
    signatory owner
    ensure balance >= 0.0

    choice Withdraw : ContractId Vault
      with amount : Decimal
      controller owner
      do
        assertMsg "insufficient balance" (amount <= balance)
        create this with balance = balance - amount


vaultTest : Script ()
vaultTest = do
  alice <- allocateParty "Alice"
  bob   <- allocateParty "Bob"

  vaultId <- submit alice do
    createCmd Vault with owner = alice; balance = 100.0

  -- ── Reject: overdraft ───────────────────────────────
  -- This should fail because 200 > 100.
  submitMustFail alice do
    exerciseCmd vaultId Withdraw with amount = 200.0

  -- ── Reject: wrong controller ────────────────────────
  -- Bob is not the owner, so he cannot exercise Withdraw.
  submitMustFail bob do
    exerciseCmd vaultId Withdraw with amount = 10.0

  -- ── Reject: negative amount violates ensure ──────────
  -- Creating a vault with negative balance fails ensure.
  submitMustFail alice do
    createCmd Vault with owner = alice; balance = -1.0

  -- ── Confirm: valid withdrawal succeeds ──────────────
  vaultId2 <- submit alice do
    exerciseCmd vaultId Withdraw with amount = 50.0

  Some vault <- queryContractId alice vaultId2
  assert (vault.balance == 50.0)

Key points

Behavior

• submitMustFail party do ... succeeds (passes) only if the ledger rejects the transaction.
• If the ledger accepts a submitMustFail submission, the script fails immediately.

Use cases

• Use submitMustFail to test: authorization violations (wrong controller), ensure failures, assert/assertMsg failures, and stale ContractId references.
• submitMustFail does not reveal the error type: it only asserts failure. To inspect the specific failure, use trySubmit.
• Testing both happy paths and failure paths is essential. The ledger silently rejects invalid transactions in production; scripts make the expectation explicit.

Syntax

• Semicolons (;) can separate record fields on one line: with owner = alice; balance = 100.0.