> ## 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.

## 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");
```

***