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Intermediate · 30 minutes

Algo Builder Tutorial Part 4: Testing Smart Contracts

This is the fourth tutorial from the Algo Builder series:



  • Good knowledge about Blockchain and Algorand.
  • Detailed introduction to algob
  • Detailed knowledge about assets, accounts, transactions and signatures.
  • Brief about Stateful Smart Contracts



TEAL is a stack based language that executes inside Algorand transactions to program logic signatures and smart contracts. @algo-builder/runtime provides a JavaScript, lightweight runtime and TEAL interpreter to test Algorand transactions, ASA and Smart Contracts.

NOTE: TEAL can not modify nor create transactions.

Algob JS Runtime Introduction

The @algo-builder/runtime (JavaScript Algorand runtime) package has 4 major components:

  • Runtime: process transaction or txn group, and manages state. algob user interacts directly with Runtime to set up accounts and post transactions (create applications, upate application, opt-in to app, ASA …).
  • AccountStore: AccountStore object represents an Alogrand compatible account, which stores all account related information (apps, assets, localState, globalState etc..).
  • Parser: parses TEAL code and returns a list of opcodes which are executable by the Interpreter. If any opcode/data in teal code is invalid, parser will throw an error.
  • Interpreter: Executes the list of opcodes returned by the parser and updates Runtime current transaction context after each opcode execution. At the end of execution, if the execution stack contains a single non-zero uint64 element then the teal code is approved, and and current transaction context is committed. If transaction is executed in a group context, then the state commit only happens if all transactions in the group pass.

Block Rounds/Height

In Algorand blockchain, transaction processing is divided into rounds. At each round blockchain creates a block with transactions which update the state. All transactions in the same block have the same transaction time and block height. In Alogrand Builder Runtime, we don’t have blocks. All transactions are processed immediately. However, we keep the notion of rounds and timestamps because it is needed for transaction and smart contract processing.

The default Runtime block round is set to 2 and timestamp to 1. Runtime doesn’t change the block round or timestamp - it’s up to the user to set in when designing a test flow. To change the block round and timestamp we need to call runtime.setRoundAndTimestamp(round, timestamp). We can retrieve the current block round and timestamp using runtime.getRound() and runtime.getTimestamp() respectively. <br />

runtime.setRoundAndTimestamp(5, 10); // set current block round to 5 and timestamp to 10

This means that current block round is set to 5 and transaction will pass only if its’ first valid round is less or equal 5 and the last valid round is greater than 5. Note: Block round and timestamp remains same until user will change it again.


Project Structure

algob project:
├── assets
│   ├── TEAL files
│   ├── PyTEAL files
├── scripts
│   ├── deploy.ts
│   ├── run.ts
├── test
│   ├── JS test files
│   ├── .mocharc.json (optional)
├── package.json

All our test files should be stored in test directory. You can import algob library as well as scripts.
Tests are typically done using Mocha framework, while assertions using Chai a BDD / TDD assertion library. Your test file is usually organized as follows:

describe("use-case", function() {
  let variabl1;
  // ...

  this.beforeAll(() => { ... });
  this.afterAll(() => { ... });

  it("test case 1", () => {
    // preparation
    // execution
    // checks

  it("test case 2", () => { ... });

Please read more about Mocha and Chai if you are not familiar with them.

Test structure

In this section we will describe the flow of testing smart contracts in runtime:

  • Prepare Accounts. First of all we need to create accounts which we will use in transactions:

const john = new AccountStore(initialMicroAlgo);
const bob = new AccountStore(initialMicroAlgo);

initialAlgo is the amount of ALGO set for the created account. It’s recommended to have at least 1 ALGO (1000000 micro ALGO) to cover transaction fees and to maintain minimum account balance.

  • Prepare Runtime. Next we create a runtime with those accounts.

const runtime = new Runtime([john, bob]);

  • Set block round and timestamp.

runtime.setRoundAndTimestamp(20, 100);

  • Create Apps/Assets. At this point our runtime is ready. Now we can create apps and assets, and begin testing our smart contracts (present in your current directory’s asset folder). To create a stateful application (smart contract), use runtime.addApp() funtcion. Similarly to create a new asset use runtime.addAsset() function.
  • Create and Execute Transactions. We can create transactions to test our smart contracts. You create a tranaction (Payment Transaction, Atomic Transfers, Asset Transfer etc…) as you would do it in algob: either using the JS SDK, or one of the high level algob functions. To execute tranasction use runtime.executeTx() funtion.
  • Update/Refresh State. After a transaction is executed the state of an account will be updated. In order to inspect a new state of accounts we need to re-query them from the runtime. In algob examples we use syncAccounts() closure (see example) closure which will reassign accounts to their latest state.
  • Verify State: Now, we can verify if the global state and local state as well as accounts are correctly updated. We use runtime.getGlobalState() and runtime.getLocalState() to check the state and directly inspect account objects (after the syncAccounts is made).

Run tests

To run your tests you may use:

mocha <test_name or path>

or you can also run tests using algob

algob test

Stateless TEAL

Escrow Account

Let’s try to execute a transaction where a user (say john) can withdraw funds from an escrow account based on a stateless smart contract logic. In the example below, we will use a TEAL code from our escrow account test.
The logic signature accepts only ALGO payment transaction where amount is <= 100 AND receiver is john AND fee <= 10000.

  • First let’s prepare the runtime and state: initialize accounts, get a logic signature for escrow and set up runtime:

const minBalance = BigInt(ALGORAND_ACCOUNT_MIN_BALANCE + 1000); // 1000 to cover fee
const initialEscrowHolding = minBalance + BigInt(1000e6);
const initialJohnHolding = minBalance + 500n;
const fee = 1000;

// admin is an account used to fund escrow
let admin = new AccountStore(1e12);
let john = new AccountStore(initialJohnHolding);
const lsig = runtime.getLogicSig(getProgram('escrow.teal'), []);
let escrow = runtime.getAccount(lsig.address());
const runtime = new Runtime([john]); // setup runtime

  • We create a helper function to update local accounts based on the runtime state

function syncAccounts() {
  john = runtime.getAccount(john.address);
  escrow = runtime.getAccount(escrow.address);

  • Execute transaction (using runtime.executeTx()) with valid txnParams.

// set up transaction paramenters
let paymentTxParams: AlgoTransferParam = {
  type: TransactionType.TransferAlgo,
  sign: SignType.LogicSignature,
  lsig: lsig,
  fromAccountAddr: escrow.address,
  toAccountAddr: john.address,
  amountMicroAlgos: 100n,
  payFlags: { totalFee: fee },

it("should fund escrow account", function(){
    type: TransactionType.TransferAlgo, // payment
    sign: SignType.SecretKey,
    fromAccount: admin.account,
    toAccountAddr: escrow.address,
    amountMicroAlgos: initialEscrowHolding,
    payFlags: { totalFee: fee },

  // check initial balance
  assert.equal(escrow.balance(), initialEscrowHolding);
  assert.equal(john.balance(), initialJohnHolding);

it("should withdraw funds from escrow if txn params are correct", function() {

  // check final state (updated accounts)
  assert.equal(escrow.balance(), initialEscrowHolding - 100n - BigInt(fee));
  assert.equal(john.balance(), initialJohnHolding + 100n);

In the first test above, we fund the escrow using the admin account. John already has an initial balance set - we initialized runtime with Johns’ account. In the second test we execute payment transaction from escrow to john and validate that the balances are correct.

  • Executing transaction with invalid transaction.

it("should reject transaction if amount > 100", function() {
    () => runtime.executeTx({...paymentTxParams, amountMicroAlgos: 500n}),

Full example with above tests is available in our escrow-account.ts integration test suite.

Delegated Signature Account

Let’s try to execute a transaction where a user (john) will use delegated signature based on a stateless smart contract logic. We will use a TEAL code from our asset test suite.

  • As before we start with preparing the runtime. We use runtime.getLogicSig(getProgram('escrow.teal'), []) to create a logic signature.

let john = new AccountStore(initialJohnHolding);
let bob = new AccountStore(initialBobHolding);
let runtime = new Runtime([john, bob]);

  • We will create a test with valid delegated signature check and try to use it to send ALGO from the delegator account.

const txnParams: ExecParams = {
  type: TransactionType.TransferAlgo, // payment
  sign: SignType.LogicSignature,
  fromAccountAddr: john.account.addr,
  toAccountAddr: bob.address,
  amountMicroAlgos: 100n,
  lsig: {} as LogicSig, // will be set below
  payFlags: { totalFee: fee }

it("should send algo's from john to bob if delegated logic check passes", function () {
  // check initial balance
  assert.equal(john.balance(), initialJohnHolding);
  assert.equal(bob.balance(), initialBobHolding);

  // get delegated logic signature
  const lsig = runtime.getLogicSig(getProgram('basic.teal'), []);
  txnParams.lsig = lsig;


  assert.equal(john.balance(), initialJohnHolding - 100n - BigInt(fee));
  assert.equal(bob.balance(), initialBobHolding + 100n);

  • In the next test, create a delegated signature which verification will fail. We check that the transfer was not done and the balances didn’t change.

it("should fail if delegated logic check doesn't pass", function () {
  const johnBal = john.balance();
  const bobBal = bob.balance();
  const lsig = runtime.getLogicSig(getProgram('incorrect-logic.teal'), []);
  txnParams.lsig = lsig;

  // should fail because logic check fails
    () => runtime.executeTx({...txnParams, amountMicroAlgos: 50n}),

  // accounts balance shouldn't be changed
  assert.equal(john.balance(), johnBal);
  assert.equal(bob.balance(), bobBal);

Full example with the above tests is available in our basic-teal integration test suite.

Stateful TEAL

Now, we will execute a transaction with an app call (stateful TEAL). The app is a simple smart contract which increments a global and local “counter” during each application call. Teal code can be found here

  • Similar to the previous test, we need to setup accounts and initialize runtime. Now, for stateful smart contract, we also need to create a new application in user account and opt-in (to call the stateful smart contract later). User can use runtime.addApp() and runtime.optInToApp() for app setup.

const john = new AccountStoreImpl(1000);
let runtime: Runtime;
let program: string;

const txnParams: ExecParams = {
  type: TransactionType.CallNoOpSSC,
  sign: SignType.SecretKey,
  fromAccount: john.account,
  appId: 0,
  payFlags: { totalFee: fee }

this.beforeAll(async function () {
  runtime = new Runtime([john]); // setup test
  program = getProgram('counter-approval.teal');

  // create new app
  txnParams.appId = await runtime.addApp({
    sender: john.account,
    globalBytes: 32,
    globalInts: 32,
    localBytes: 8,
    localInts: 8
  }, {}, program);

  // opt-in to the app
  await runtime.optInToApp(txnParams.appId, john.address, {}, {}, program);

  • After set up, let’s call the stateful smart contract and check the updated global state

const key = "counter";
it("should set global and local counter to 1 on first call", function () {

  const globalCounter = runtime.getGlobalState(txnParams.appId, key);
  assert.equal(globalCounter, 1n);

  const localCounter = runtime.getAccount(john.address).getLocalState(txnParams.appId, key); // get local value from john account
  assert.equal(localCounter, 1n);

In this test, after executing a transaction with stateful smart contract call, we are verifying if the global state and local state are updated correctly. User can use runtime.getGlobalState() and runtime.getLocalState() to check state.

Please look at stateful-counter.ts to see the complete integration test suite.

Best Practices

  • Follow the Test Structure section to setup your tests.
  • Structure tests using AAA pattern: Arrange, Act & Assert (AAA). The first part includes the test setup, then the execution of the unit under test, and finally the assertion phase. Following this structure guarantees that the reader will quickly understand the test plan.
  • To prevent test coupling and easily reason about the test flow, each test should add and act on its own set of states.
  • Use beforeEach, afterEach, beforeAll, afterAll functions to setup and clean shared resources in your tests.
  • Sync your accounts’ before checking their state.


TEAL files used for the below tests can be found in /test/fixtures in runtime package.

See our examples for more interesting test suites.

May 20, 2021