Add fuzz tests for ShortString (#4175)

test/utils/ShortStrings.t.sol

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "forge-std/Test.sol";
+
+import "../../contracts/utils/ShortStrings.sol";
+
+contract ShortStringsTest is Test {
+    string _fallback;
+
+    function testRoundtripShort(string memory input) external {
+        vm.assume(_isShort(input));
+        ShortString short = ShortStrings.toShortString(input);
+        string memory output = ShortStrings.toString(short);
+        assertEq(input, output);
+    }
+
+    function testRoundtripWithFallback(string memory input, string memory fallbackInitial) external {
+        _fallback = fallbackInitial; // Make sure that the initial value has no effect
+        ShortString short = ShortStrings.toShortStringWithFallback(input, _fallback);
+        string memory output = ShortStrings.toStringWithFallback(short, _fallback);
+        assertEq(input, output);
+    }
+
+    function testRevertLong(string memory input) external {
+        vm.assume(!_isShort(input));
+        vm.expectRevert(abi.encodeWithSelector(ShortStrings.StringTooLong.selector, input));
+        this.toShortString(input);
+    }
+
+    function testLengthShort(string memory input) external {
+        vm.assume(_isShort(input));
+        uint256 inputLength = bytes(input).length;
+        ShortString short = ShortStrings.toShortString(input);
+        uint256 shortLength = ShortStrings.byteLength(short);
+        assertEq(inputLength, shortLength);
+    }
+
+    function testLengthWithFallback(string memory input, string memory fallbackInitial) external {
+        _fallback = fallbackInitial;
+        uint256 inputLength = bytes(input).length;
+        ShortString short = ShortStrings.toShortStringWithFallback(input, _fallback);
+        uint256 shortLength = ShortStrings.byteLengthWithFallback(short, _fallback);
+        assertEq(inputLength, shortLength);
+    }
+
+    function toShortString(string memory input) external pure returns (ShortString) {
+        return ShortStrings.toShortString(input);
+    }
+
+    function _isShort(string memory input) internal pure returns (bool) {
+        return bytes(input).length < 32;
+    }
+}