How do we get the balance of a test account in SmartPy?

Question

I am transferring some tez to an account and i want to assert balance of account before and after the transfer. How do i get the balance of test account in SmartPy.

Answer 1

There is no way to get the balance of test accounts.

You can replace the test account by a contract with an entrypoint named default. You can set the contract's initial value and compare its balance as it is a contract.

import smartpy as sp

class MyContract(sp.Contract):
    @sp.entry_point
    def send_tez(self, destination, amount):
        sp.send(destination, amount)


class Receiver(sp.Contract):
    @sp.entry_point
    def default(self):
        pass

@sp.add_test(name = "Test")
def test():
    sc = sp.test_scenario()
    c1 = MyContract()
    c1.set_initial_balance(sp.tez(42))
    sc += c1
    c2 = Receiver()
    c2.set_initial_balance(sp.tez(0))
    sc += c2
    c1.send_tez(destination=c2.address, amount=sp.tez(10))
    sc.show(c2.balance)

Answer 2

You can do so using sp.verify and .balance

import smartpy as sp

class MyContract(sp.Contract):
    def __init__(self, **kargs):
        self.init(**kargs)

@sp.add_test(name = "First test")
def test():
    sc = sp.test_scenario()
    c1 = MyContract()
    sc += c1
    # and its balance
    sc.verify(c1.balance == sp.tez(0))

Answer 3

It is not possible to get the balance of an implicit account from the execution context of a smart contract in general, so I don't think SmartPy would include such a feature.
It doesn't really make sense to compare balances because, when you transfer tez at the end of the execution of the contract, the balance of the implicit account will only be updated AFTER the contract finished executing (because of the order of execution of the operations). The contract has to finish executing first before any side effects are saved in the blockchain, including tez transfers or even updates of its own storage!