Foundry test: introduction

src/HelloWorld.sol

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+pragma solidity ^0.8.20;
+
+contract HelloWorld {
+    string public greet = "Hello World!";
+}

test/HelloWorld.t.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.13;
+
+import {Test, console2} from "forge-std/Test.sol";
+import {HelloWorld} from "../src/HelloWorld.sol";
+
+contract CounterTest is Test {
+    HelloWorld public helloWorld;
+
+    function setUp() public {
+        helloWorld = new HelloWorld();
+    }
+
+    function testGreet() public {
+        assertEq(
+            helloWorld.greet(),
+            "Hello World!"
+        );
+    }
+
+}