How to QA Smart Contracts on Blockchain

Published: Apr 19, 2024

Deploying a smart contract on the public blockchain is a significant milestone, but it's also fraught with risk. The immutability of blockchain technology means that any flaws in the contract's code can have irreversible consequences. In this guide, we will walk you through a systematic and detailed approach to ensure that your smart contract functions as intended, remains secure against malicious attacks, and is optimized for performance and cost-effectiveness.

  • Lily HuLily Hu / Smart Contract Engineer


Deploying a smart contract is a significant milestone in the life cycle of blockchain development, but it's also a moment fraught with risk if not approached with meticulous care. The immutability of blockchain technology means that any flaws in the contract's code can have irreversible consequences. This is why quality assurance is not just a routine checkpoint, but the backbone of a successful smart contract launch.

In this guide, we will walk you through a systematic and detailed approach to ensure that your smart contract functions as intended, remains secure against malicious attacks, and is optimized for performance and cost-effectiveness.

Main Workflow:


Static Analysis

Use tools like Slither, Solhint, or MythX to analyze the smart contracts for common vulnerabilities and coding mistakes, such as reentrancy, integer overflow, and denial of service attacks.

  • Slither: The Slither framework provides automated vulnerability and optimization detection, as well as assistive codebase summaries to further developer comprehension.
  • Solhint: Solhint detects a wide array of validation and security rules in compliance with Solidity's style guide.
  • Mythx: A security analysis service for Ethereum smart contracts

Mythx Analysis Result:



Smart contract testing is a critical process that involves scrutinizing the code and logic of smart contracts to ensure they operate accurately and securely. Since smart contracts automate transactions and enforce agreements on the blockchain without third-party oversight, it's essential that they run without flaws or vulnerabilities.

Unit Testing

Smart contract unit tests are a type of software testing where individual units, functions, or components of a smart contract are tested in isolation to ensure that each part works correctly on its own. It is primarily conducted by the developers of the contract.

These tests are key for identifying flaws within the smallest testable parts of a contract, helping to prevent bugs that could lead to security breaches or functional errors. By testing each unit separately, developers can catch and fix problems early in the development process, which can save time, reduce costs, and enhance the security and reliability of the final smart contract.

The smart contract unit testing landscape is dominated by a variety of tools, each offering distinct features to streamline the development process. Prominent among these are Hardhat, Foundry, Brownie, Waffle, and Truffle.

Fuzzing Testing

Fuzzing is particularly useful for uncovering hidden problems, such as those that could be exploited by malicious actors (e.g., hackers) to compromise the contract or the funds it handles. It's an essential part of ensuring that smart contracts are robust and secure before they are deployed on the blockchain.

The fuzz testing tool that is currently popular among developers is Foundry.

Integration Testing

  1. Checking that multiple contracts work well together, for example, one contract might hold funds while another manages the rules for transferring those funds.
  2. Ensuring that the contract interactions with the blockchain (such as recording transactions or checking balances) occur without errors.
  3. Verifying that the contract's functions interact with external systems or oracles correctly if they depend on external data.

Integration tests are crucial because they can catch issues that are not visible in unit tests. Integration testing shares tooling with unit testing, yet demands a more sophisticated testing environment. Generally, it necessitates mirroring the main network locally through forking for comprehensive testing. Forking functions are also featured within the Hardhat, Foundry, and Brownie development environments.

Security Testing

Particularly important due to the high-value assets often managed by contracts; this step involves identifying potential security vulnerabilities.

Upgradability and Migrations Testing

If your contract is designed to be upgradable or requires migrations, test these mechanisms thoroughly to check that the contract's code and data can be updated or migrated smoothly to a new version without losing functionality or causing disruption to users.

By undergoing rigorous testing, smart contracts can be trusted to manage transactions and execute terms autonomously on the blockchain with reduced risk of hacks, funds loss, or unintended consequences.

  • Hardhat:
    Is one of the most popular programming environments based on Javascript for developing Ethereum-based decentralized applications.
  • Foundry:
    Is a convenient Ethereum application development toolkit written in Rust.Foundry is rapid, modular and portable. Essentially, Foundry is a reinvention of the testing framework.
  • Brownie:
    Is a Python-based testing framework for smart contracts targeting blockchains that operate an Ethereum Virtual Machine. It allows developers to run tests before deploying contracts on EVM-compatible networks.
  • Waffle:
    Typescript-compatible smart contract testing library for Ethereum that works with ethers.js.
  • Truffle:
    Is the leading Ethereum development environment to build, deploy and test smart contracts. (The Truffle suite is being phased out; we advise against using it moving forward)

Gas Consumption Analysis

Gas Consumption Analysis refers to the process of evaluating the amount of gas required for executing operations within a smart contract on the Ethereum blockchain. This analysis is crucial to optimize efficiency and cost-effectiveness, as gas fees impact the overall expense for users interacting with the contract. Developers perform gas consumption analysis to reduce unnecessary computational work, streamline contract functions, and ensure economic viability of transactions for end users. Both Hardhat and Foundry are equipped with features that can analyze gas usage for smart contracts.

Hardhat-gas-reporter Result:



Once the preliminary testing phases have been finished, it's advisable to engage expert security auditors to meticulously examine your code. This step helps identify any potential security flaws that automated testing tools might have overlooked.

Here are some prominent audit firms specializing in smart contract security that have gained recognition in the blockchain community: Trail of Bits, Spearbit, PeckShield, Secure3, OpenZeppelin……

  • Trail of Bits:
    Is a blockchain auditing company and open source web3 security tool developer offering a variety of services and products. Trail of Bits helps blockchain companies harden smart contracts, understand contract storage and manage, and identify many potential vulnerabilities
  • Spearbit:
    Is a decentralized network of security experts that offer web3 security consulting services. Spearbit offers one-off security reviews by a hand-selected team of experts and recurring security reviews in the form of retainer agreements.
  • PeckShield:
    Is a blockchain security firm offering audits, pen tests, threat monitoring, and more.

TestNet Deployment

Launch your contract on a public Ethereum test network, such as Sepolia, Goerli and Holesky, to test under conditions that closely resemble the actual environment, including aspects like network delays and interactions with various transactions and contracts. This is a critical phase to verify the contract's performance in an ecosystem that simulates the main network's operation.

PreRelease Deployment

In cases where certain contracts need to interface with third-party contracts not available on TestNets, deploying your smart contracts on the Mainnet becomes necessary for final testing. This step is crucial to confirm that they function correctly in the live environment as anticipated.

Mainnet Deployment

Once you've completed testing on the TestNet, you're ready to deploy your smart contracts on the Mainnet to serve the end users. After deployment you should verify smart contracts.

Verify Contracts

Verifying a contract involves ensuring that its source code can be compiled to produce the same bytecode that is present on the blockchain. When using Etherscan, if successful, the contract's source code will be displayed under the "Contract" tab, confirming that it matches the on-chain bytecode.

Etherscan Contract Tab:


The majority of integrated development environments are equipped with features that enable the deployment and verification of smart contracts, such as those provided by Hardhat, Foundry, and Brownie.

Bug Bounties and Public Review

After deploying the smart contracts to the Mainnet, it may be advantageous to initiate a bug bounty program, thereby encouraging the wider community to examine your code. This incentivizes external security experts and enthusiasts to identify and report any residual bugs or security vulnerabilities that internal testing may have missed. A widely recognized tool for bug bounty programs in the realm of smart contracts is Immunefi.

  • Immunefi: Is the premier bug bounty platform for smart contracts and DeFi projects, where security researchers review code, disclose vulnerabilities, get paid, and make crypto safer.

Immunefi Bounty List:


Monitor Performance

Employ tracking tools such as Tenderly, Forta, or Etherscan to maintain vigilance over your contract's activities. These services provide notifications for any anomalous actions that could indicate potential security issues.

  • Tenderly:
    Ethereum developer platform for real-time monitoring, debugging, and simulating smart contracts.
  • Forta:
    Is a real-time decentralized cybersecurity network running on Ethereum, Polygon, and multiple other blockchains.
  • Etherscan:
    Is an Ethereum block explorer and analytics platform. Users can see and analyze assets, balances and transactions on the Ethereum network. Developers can interact with smart contracts and view gas prices on Etherscan.

Tenderly Tool Categories:


As we wrap up this guide on deploying smart contracts with quality assurance, remember that the effort you put in now lays the foundation for your contract's success. Following these steps greatly reduces the risk of errors and ensures your contract stands ready for real-world use.

Keep in mind that deployment is just the beginning. Your smart contract will start its journey in the wider blockchain ecosystem, interacting with users and possibly other contracts. Stay vigilant, and continue to monitor and improve your contract as needed. With this solid approach, you're now ready to confidently launch your smart contract into the world. Good luck!

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