Test with Foundry

Prerequisites

You should already have a Foundry project set up, and have compiled your smart contract successfully. See the set up Foundry and compile a smart contract tutorial for how to do so.

Edit the test specifications

As the smart contract we are testing is minimal, so are the test cases that it needs.

Before testing, we need to deploy the smart contract. This happens in the setUp block. This is because smart contracts cannot execute in isolation, they must be within the EVM to execute. In Foundry, by default, the tests will execute in an emulated in-memory EVM instance, which is transient, so the deployment is perfunctory.

Open the file: test/Counter.t.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.28;

import { Test } from "forge-std/Test.sol";
import { Counter } from "../src/Counter.sol";

contract CounterTest is Test {
    Counter public counter;

    function setUp() public {
        counter = new Counter();
    }

    function testInitialValue() public view {
        assertEq(counter.value(), 0);
    }

    function testIncrementValueFromZero() public {
        counter.increment(100);
        assertEq(counter.value(), 100);
    }

    function testIncrementValueFromNonZero() public {
        counter.increment(100);
        counter.increment(23);
        assertEq(counter.value(), 123);
    }
}

We see that there are 3 test cases:

• Check the initial value().

• Invoke increment(num) and then check that the value() has updated.

• Invoke increment(num) again, and then check that the value() has updated again.

Execute tests against the smart contract

The following command runs the tests we just looked at.

forge test

Check the test output

If all the tests work as planned, you should see some output similar to the following:

Ran 3 tests for test/Counter.t.sol:CounterTest
[PASS] testIncrementValueFromNonZero() (gas: 32298)
[PASS] testIncrementValueFromZero() (gas: 31329)
[PASS] testInitialValue() (gas: 10392)
Suite result: ok. 3 passed; 0 failed; 0 skipped; finished in 5.35ms (3.16ms CPU time)

Ran 1 test suite in 171.04ms (5.35ms CPU time): 3 tests passed, 0 failed, 0 skipped (3 total tests)

Next steps

Now that you have tested your smart contract, you are ready to deploy that smart contract! Check out the deploy a smart contract using Foundry tutorial next.