# Forge Standard Library • [![tests](https://github.com/brockelmore/forge-std/actions/workflows/tests.yml/badge.svg)](https://github.com/brockelmore/forge-std/actions/workflows/tests.yml)

Forge Standard Library is a collection of helpful contracts for use with [`forge` and `foundry`](https://github.com/foundry-rs/foundry). It leverages `forge`'s cheatcodes to make writing tests easier and faster, while improving the UX of cheatcodes.

**Learn how to use Forge Std with the [📖 Foundry Book (Forge Std Guide)](https://book.getfoundry.sh/forge/forge-std.html).**

## Install

```bash
forge install foundry-rs/forge-std
```

## Contracts

### stdError

This is a helper contract for errors and reverts. In `forge`, this contract is particularly helpful for the `expectRevert` cheatcode, as it provides all compiler builtin errors.

See the contract itself for all error codes.

#### Example usage

```solidity
import 'forge-std/Test.sol';

contract TestContract is Test {
  ErrorsTest test;

  function setUp() public {
    test = new ErrorsTest();
  }

  function testExpectArithmetic() public {
    vm.expectRevert(stdError.arithmeticError);
    test.arithmeticError(10);
  }
}

contract ErrorsTest {
  function arithmeticError(uint256 a) public {
    uint256 a = a - 100;
  }
}

```

### stdStorage

This is a rather large contract due to all of the overloading to make the UX decent. Primarily, it is a wrapper around the `record` and `accesses` cheatcodes. It can _always_ find and write the storage slot(s) associated with a particular variable without knowing the storage layout. The one _major_ caveat to this is while a slot can be found for packed storage variables, we can't write to that variable safely. If a user tries to write to a packed slot, the execution throws an error, unless it is uninitialized (`bytes32(0)`).

This works by recording all `SLOAD`s and `SSTORE`s during a function call. If there is a single slot read or written to, it immediately returns the slot. Otherwise, behind the scenes, we iterate through and check each one (assuming the user passed in a `depth` parameter). If the variable is a struct, you can pass in a `depth` parameter which is basically the field depth.

I.e.:

```solidity
struct T {
  // depth 0
  uint256 a;
  // depth 1
  uint256 b;
}

```

#### Example usage

```solidity
import 'forge-std/Test.sol';

contract TestContract is Test {
  using stdStorage for StdStorage;

  Storage test;

  function setUp() public {
    test = new Storage();
  }

  function testFindExists() public {
    // Lets say we want to find the slot for the public
    // variable `exists`. We just pass in the function selector
    // to the `find` command
    uint256 slot = stdstore.target(address(test)).sig('exists()').find();
    assertEq(slot, 0);
  }

  function testWriteExists() public {
    // Lets say we want to write to the slot for the public
    // variable `exists`. We just pass in the function selector
    // to the `checked_write` command
    stdstore.target(address(test)).sig('exists()').checked_write(100);
    assertEq(test.exists(), 100);
  }

  // It supports arbitrary storage layouts, like assembly based storage locations
  function testFindHidden() public {
    // `hidden` is a random hash of a bytes, iteration through slots would
    // not find it. Our mechanism does
    // Also, you can use the selector instead of a string
    uint256 slot = stdstore
      .target(address(test))
      .sig(test.hidden.selector)
      .find();
    assertEq(slot, uint256(keccak256('my.random.var')));
  }

  // If targeting a mapping, you have to pass in the keys necessary to perform the find
  // i.e.:
  function testFindMapping() public {
    uint256 slot = stdstore
      .target(address(test))
      .sig(test.map_addr.selector)
      .with_key(address(this))
      .find();
    // in the `Storage` constructor, we wrote that this address' value was 1 in the map
    // so when we load the slot, we expect it to be 1
    assertEq(uint256(vm.load(address(test), bytes32(slot))), 1);
  }

  // If the target is a struct, you can specify the field depth:
  function testFindStruct() public {
    // NOTE: see the depth parameter - 0 means 0th field, 1 means 1st field, etc.
    uint256 slot_for_a_field = stdstore
      .target(address(test))
      .sig(test.basicStruct.selector)
      .depth(0)
      .find();

    uint256 slot_for_b_field = stdstore
      .target(address(test))
      .sig(test.basicStruct.selector)
      .depth(1)
      .find();

    assertEq(uint256(vm.load(address(test), bytes32(slot_for_a_field))), 1);
    assertEq(uint256(vm.load(address(test), bytes32(slot_for_b_field))), 2);
  }
}

// A complex storage contract
contract Storage {
  struct UnpackedStruct {
    uint256 a;
    uint256 b;
  }

  constructor() {
    map_addr[msg.sender] = 1;
  }

  uint256 public exists = 1;
  mapping(address => uint256) public map_addr;
  // mapping(address => Packed) public map_packed;
  mapping(address => UnpackedStruct) public map_struct;
  mapping(address => mapping(address => uint256)) public deep_map;
  mapping(address => mapping(address => UnpackedStruct)) public deep_map_struct;
  UnpackedStruct public basicStruct = UnpackedStruct({ a: 1, b: 2 });

  function hidden() public view returns (bytes32 t) {
    // an extremely hidden storage slot
    bytes32 slot = keccak256('my.random.var');
    assembly {
      t := sload(slot)
    }
  }
}

```

### stdCheats

This is a wrapper over miscellaneous cheatcodes that need wrappers to be more dev friendly. Currently there are only functions related to `prank`. In general, users may expect ETH to be put into an address on `prank`, but this is not the case for safety reasons. Explicitly this `hoax` function should only be used for address that have expected balances as it will get overwritten. If an address already has ETH, you should just use `prank`. If you want to change that balance explicitly, just use `deal`. If you want to do both, `hoax` is also right for you.

#### Example usage:

```solidity
// SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.0;

import 'forge-std/Test.sol';

// Inherit the stdCheats
contract StdCheatsTest is Test {
  Bar test;

  function setUp() public {
    test = new Bar();
  }

  function testHoax() public {
    // we call `hoax`, which gives the target address
    // eth and then calls `prank`
    hoax(address(1337));
    test.bar{ value: 100 }(address(1337));

    // overloaded to allow you to specify how much eth to
    // initialize the address with
    hoax(address(1337), 1);
    test.bar{ value: 1 }(address(1337));
  }

  function testStartHoax() public {
    // we call `startHoax`, which gives the target address
    // eth and then calls `startPrank`
    //
    // it is also overloaded so that you can specify an eth amount
    startHoax(address(1337));
    test.bar{ value: 100 }(address(1337));
    test.bar{ value: 100 }(address(1337));
    vm.stopPrank();
    test.bar(address(this));
  }
}

contract Bar {
  function bar(address expectedSender) public payable {
    require(msg.sender == expectedSender, '!prank');
  }
}

```

### Std Assertions

Expand upon the assertion functions from the `DSTest` library.

### `console.log`

Usage follows the same format as [Hardhat](https://hardhat.org/hardhat-network/reference/#console-log).
It's recommended to use `console2.sol` as shown below, as this will show the decoded logs in Forge traces.

```solidity
// import it indirectly via Test.sol
import "forge-std/Test.sol";
// or directly import it
import "forge-std/console2.sol";
...
console2.log(someValue);
```

If you need compatibility with Hardhat, you must use the standard `console.sol` instead.
Due to a bug in `console.sol`, logs that use `uint256` or `int256` types will not be properly decoded in Forge traces.

```solidity
// import it indirectly via Test.sol
import "forge-std/Test.sol";
// or directly import it
import "forge-std/console.sol";
...
console.log(someValue);
```