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how_to_test.md

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title Testing Smart Contracts
tags
contracts
tests
sidebar_position 8
description Learn how to write and run tests for your Aztec smart contracts using Aztec.js and a local network.

This guide covers how to test Aztec smart contracts by connecting to a local network, deploying contracts, and verifying their behavior.

Prerequisites

Setting up the test environment

Connect to your local Aztec network and create an embedded wallet:

#include_code connect_to_network /docs/examples/ts/aztecjs_connection/index.ts typescript

The EmbeddedWallet manages accounts, tracks deployed contracts, and handles transaction proving. It connects to the Aztec node which provides access to both the Private eXecution Environment (PXE) and the network.

Loading test accounts

The local network comes with pre-funded accounts. Load them into your wallet:

#include_code load_test_accounts /docs/examples/ts/aztecjs_testing/index.ts typescript

Deploying contracts in tests

Deploy contracts using the generated contract class:

#include_code deploy_test_contract /docs/examples/ts/aztecjs_testing/index.ts typescript

Verifying contract state

Use .simulate() to read contract state without creating a transaction:

#include_code simulate_function /docs/examples/ts/aztecjs_connection/index.ts typescript

Simulations are free (no gas cost) and return the function's result directly. Use them for:

  • Checking balances and state before/after transactions
  • Validating expected outcomes in assertions
  • Debugging contract behavior

Sending test transactions

Send transactions and wait for confirmation:

#include_code send_transaction /docs/examples/ts/aztecjs_connection/index.ts typescript

The send() method returns when the transaction is included in a block.

Example test structure

Here's a complete test example showing the typical structure with setup, test cases, and assertions:

#include_code complete_test_example /docs/examples/ts/aztecjs_testing/index.ts typescript

Testing failure cases

Test that invalid operations revert as expected:

#include_code test_revert_case /docs/examples/ts/aztecjs_testing/index.ts typescript

Use .simulate() to test reverts without spending gas. The simulation will throw if the transaction would fail onchain.

Simulating with overrides

.simulate() accepts an overrides option that injects values into the simulator's (ephemeral) world-state fork and contract DB before the call runs. The override is scoped to that single simulation and thrown away afterwards.

Override a public-storage slot:

const result = await contract.methods.read_balance(account).simulate({
  overrides: {
    publicStorage: [{ contract: contract.address, slot: BALANCE_SLOT, value: new Fr(1_000_000n) }],
  },
});

Use this to set up state preconditions, reproduce production bugs against pinned storage, or exercise rare value branches without orchestrating the contract calls that produce them.

Further reading