> ## 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");
```

***