✅Console Log

We can use console.log() to print out debugging info in Foundry just like in JavaScript. Import the following library:

import "forge-std/console.sol";

Use console.log() in contract:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

import "forge-std/console.sol";

contract Counter {
    uint public count;

    // Function to get the current count
    function get() public view returns (uint) {
        return count;
    }

    // Function to increment count by 1
    function inc() public {
        console.log("Calling inc(). Now count = ", count);
        count += 1;
    }

    // Function to decrement count by 1
    function dec() public {
        // This function will fail if count = 0
        count -= 1;
    }
}

Verbosity at least -vv must be used to print out console.log() messages:

forge test --match-path test/Counter.t.sol -vv

console.log() in contract

Of course you can also use console.log() in test file. For example, create a test file Console.t.sol:

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

import "forge-std/Test.sol";

contract ConsoleTest is Test {
    function testLogSomething() view public {
        console.log("Log something here", 123);
    }
}

No need to import forge-std/console.sol because it is included in forge-std/Test.sol, which is already imported.

Run test with -vv verbosity:

forge test --match-path test/Console.t.sol -vv

console.log() in test file

One caveat here: console.log() can not log int. There is another function named console.logInt() for doing this job:

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

import "forge-std/Test.sol";

contract ConsoleTest is Test {
    function testLogSomething() view public {
        console.log("Log something here", 123);

        int x = -1;
        console.logInt(x);
    }
}

console.logInt()