> ## Documentation Index > Fetch the complete documentation index at: https://docs.cosmos.network/llms.txt > Use this file to discover all available pages before exploring further. # 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:** ```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}} # 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:** ```bash theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}} # 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:** ```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}} // 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. ```solidity title="test/MyContract.t.sol (Foundry)" lines expandable theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}} // 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 ```js lines expandable theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}} 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"); ``` ***