# How to Write Basic Tests {% embed url="" %} How to Write Basic Tests {% endembed %} ## Test Setup We are going to write tests for a simple counter contract: {% embed url="" %} First Application {% endembed %} Overwrite `Counter.sol` with this contract: ```solidity // SPDX-License-Identifier: MIT pragma solidity ^0.8.17; 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 { count += 1; } // Function to decrement count by 1 function dec() public { // This function will fail if count = 0 count -= 1; } } ``` Write test file `Counter.t.sol`: ```solidity // SPDX-License-Identifier: UNLICENSED pragma solidity ^0.8.13; import "forge-std/Test.sol"; import "../src/Counter.sol"; contract CounterTest is Test { Counter public counter; function setUp() public { counter = new Counter(); } function testInc() public { counter.inc(); assertEq(counter.count(), 1); } } ```

## Test for error Let's write a test case that fails. Note that `setup()` will be executed before executing each test case, so the `counter` contract in the new test case is brand new. It has nothing to do with the operations we have done in the former test case `testInc()`. ```solidity function testFailDec() public { counter.dec(); } ```

This new test case shows "PASS" because the `testFail` prefix tests for failure. A failed `testFail` case will pass. ## vm.expectRevert We can also specify expected revert reason in the test case: ```solidity function testDecUnderflow() public { vm.expectRevert(stdError.arithmeticError); counter.dec(); } ``` In this case we are testing for integer underflow.

Add one more test case: ```solidity function testDec() public { counter.inc(); counter.inc(); counter.dec(); assertEq(counter.count(), 1); } ``` ## Gas Report ```bash forge test --match-path test/Counter.t.sol --gas-report ```