Popular Libraries for Development, Testing & Fuzzing

Key frameworks, libraries, and practices for frontend development, wallet integration, smart contracts, testing and more.

Common Libraries & Tooling

These libraries are used across the stack to write tests, simulate transactions, connect wallets, and interface with the blockchain in both scripting and frontend contexts.

Library	Purpose	Key Features
Ethers.js	Contract interaction, transaction signing, provider management in JS/TS environments	Provides Contract, Provider, Wallet, and Interface abstractions. Deep Hardhat integration. ABI coder, calldata utilities, and ENS support.
Viem	Modular TypeScript-first library for RPC, contract access, encoding, and data formatting	Tree-shakeable. Supports batching, client-side caching, EIP-1559 fees, multicalls, typed reads/writes. Used by Wagmi.
Wagmi	React hooks for wallet connection, chain state, and contract calls in frontend apps	Built on Viem. Includes useAccount, useConnect, useContractRead, and event subscriptions. Enables seamless integration with wallet modals.
Web3.js	Legacy Ethereum contract and RPC library	One of the earliest libraries. Now largely unmaintained. Lacks EIP-1559 support and modern modularity.
RainbowKit	React component library for wallet connection UI and chain management	Pre-built wallet connect buttons, chain switch UI, and custom themes. Integrates with Wagmi for wallet state management and tx handling.

Ethers and Viem serve similar purposes, but Viem is optimized for frontend apps. Wagmi builds on Viem. Web3.js is no longer recommended for new projects.

---

Testing Frameworks

Note Smart contract quality and security depend on a comprehensive testing strategy including but not limited to:

• Unit Tests: Verify individual functions and components
• Property-Based Fuzzing: Test invariants with random inputs
• Code Coverage: Ensure all code paths are tested
• Static Analysis: Detect common vulnerabilities and anti-patterns

The tools and frameworks below provide a foundation for each of these testing layers.

Foundry — Solidity-Native

• Tests written directly in Solidity.
• Very fast runner (forge test) and rich cheatcodes for state manipulation.
• Built-in, configurable fuzzing (forge test --fuzz-runs=N).
• Includes tools like forge script, forge coverage, and forge snapshot.

Hardhat — JavaScript / TypeScript

• Mocha + Chai test runner for JS/TS-based tests.
• Flexible task system (hardhat.config.js), plugin support, and network forking.
• Integrates with Ethers.js and Solidity tooling for deployments, gas tracking, and test orchestration.

v0.5.0 Compatibility Testing Framework

Cosmos EVM v0.5.0 introduces comprehensive compatibility testing to ensure seamless integration with major Ethereum development tools.

EVM Tools Compatibility Testing

Automated Testing Suites: Five comprehensive test suites validate compatibility with popular Ethereum tools:

Tool	Test Coverage	GitHub Workflow
Foundry	Contract deployment, testing, gas estimation	.github/workflows/tests-compatibility-foundry.yml
Hardhat	Contract deployment, ethers.js integration	.github/workflows/tests-compatibility-hardhat.yml
Viem	TypeScript client compatibility, RPC methods	.github/workflows/tests-compatibility-viem.yml
Web3.js	Legacy client compatibility, transaction handling	.github/workflows/tests-compatibility-web3js.yml
Foundry + UniswapV3	Complex DeFi protocol deployment	.github/workflows/tests-compatibility-foundry-uniswap-v3.yml

Running Compatibility Tests

Local Testing:

# Run JSON-RPC compatibility tests
cd /path/to/cosmos-evm
make test-rpc-compat  # Makefile:373

# Test specific tool
./scripts/tests_compatibility_foundry.sh
./scripts/tests_compatibility_hardhat.sh
./scripts/tests_compatibility_viem.sh
./scripts/tests_compatibility_web3js.sh
./scripts/tests_compatibility_foundry_uniswap_v3.sh

Test Structure:

tests/evm-tools-compatibility/
├── foundry/          # Foundry compatibility tests
├── hardhat/          # Hardhat + Ethers.js tests
├── viem/             # Viem TypeScript tests
├── web3.js/          # Web3.js legacy tests
└── foundry-uniswap-v3/ # Complex DeFi protocol tests

JSON-RPC Compatibility Testing

Comprehensive RPC Validation: New framework compares Cosmos EVM responses against geth for accuracy.

Setup:

# Start comparison testing environment
cd tests/jsonrpc

# Build required Docker images
make localnet-build-env

# Start both evmd and geth for comparison
./scripts/start-networks.sh

# Run compatibility test suite
cd simulator && go build . && ./simulator

# Stop testing environment
./scripts/stop-networks.sh

Test Coverage:

• Transaction Processing: Compare transaction execution results
• Block Queries: Validate block structure and data
• Account Queries: Verify balance and nonce handling
• Event Logs: Ensure log filtering and retrieval accuracy
• Gas Estimation: Compare gas estimation algorithms

Configuration:

// tests/jsonrpc/simulator/config/config.go:27-36
type Config struct {
    EvmdHttpEndpoint string // Default: "http://localhost:8545"
    EvmdWsEndpoint   string // Default: "ws://localhost:8546"
    GethHttpEndpoint string // Default: "http://localhost:8547"
    GethWsEndpoint   string // Default: "ws://localhost:8548"
    RichPrivKey      string
    Timeout          string
}

Fuzz (Property-Based) Testing

Fuzz testing generates random inputs to find edge cases that violate expected properties.

test/MyContract.t.sol (Foundry)

// test/MyContract.t.sol  (Foundry)
function test_myFunction_fuzz(uint256 amount) public {
    vm.assume(amount > 0 && amount < 1e18);   // constrain input
    myContract.myFunction(amount);
    assertEq(myContract.someState(), expectedValue);
}

Tool	Notes
Foundry	Built-in fuzzing; enabled by default when running forge test.
Echidna	External, property-based fuzzer. Supports invariants and campaigns.

Use fuzzing to test against invariants such as:

• balance never exceeds total supply
• no overflow or underflow under bounded inputs
• access control is consistently enforced

Supplementary Tools

Tools that enhance test coverage, assert correctness, or catch common vulnerabilities.

Tool	Purpose	Typical Command
OpenZeppelin Test Helpers	Time travel, event assertions, reverts	JS/TS only. Works with Hardhat + Mocha.
solidity-coverage	Reports untested branches in Solidity	npx hardhat coverage · forge coverage
Slither	Static analysis for known vuln patterns	slither .

Example — OpenZeppelin Test Helpers

const { time, expectRevert } = require('@openzeppelin/test-helpers');

// advance clock by one day
await time.increase(time.duration.days(1));

// expect revert with specific reason
await expectRevert(contract.someFunction(), "Ownable: caller is not the owner");

---