bug.pact

(update accounts from { "balance": (- from-bal amount) })
(update accounts to   { "balance": (+ to-bal amount) })))

;; 

(update accounts "brian" { "balance": (- previous-balance 1000000) })
(update accounts "brian" { "balance": (+ previous-balance 1000000) })

test.pact

(enforce-pact-version "2.4.1")

(define-keyset 'accounts-admin-keyset
  (read-keyset "accounts-admin-keyset"))

(module accounts 'accounts-admin-keyset
  "Demo module"

  (defschema account
    ("account"
      (invariant (>= balance 0)))
    balance:integer
    ks:keyset)
  (deftable accounts:{account})

(defun transfer (from:string to:string amount:integer)
  ("Transfer money between accounts"
    (properties [
      (row-enforced 'accounts 'ks from)
      (= (column-delta 'accounts 'balance) 0)
      ]))

  (let ((from-bal (at 'balance (read accounts from)))
        (from-ks  (at 'ks      (read accounts from)))
        (to-bal   (at 'balance (read accounts to))))
    (enforce-keyset from-ks)
    (enforce (> amount 0))
    (enforce (>= from-bal amount) "Insufficient Funds")
    (enforce (!= to from))
    (update accounts from { "balance": (- from-bal amount) })
    (update accounts to   { "balance": (+ to-bal amount) }))))

test.repl

(env-keys ["accountadmin" "user123" "user456"])
(env-data { "accounts-admin-keyset": ["accountadmin"] })
(begin-tx)
(load "test.pact")
(commit-tx)
(verify 'accounts)