test: add tests for Buffer

test/unit/libraries/Buffer.t.sol

@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.0;
+
+import "forge-std/Test.sol";
+
+import { Buffer } from "src/libraries/Buffer.sol";
+
+contract BufferTest is Test {
+    using Buffer for uint16;
+
+    function testPrev_AtLimit() external {
+        // arrange
+        uint16 lIndex = 0;
+
+        // act & assert
+        assertEq(lIndex.prev(), Buffer.SIZE - 1);
+    }
+
+    function testNext_AtLimit() external {
+        // arrange
+        uint16 lLimit = Buffer.SIZE - 1;
+
+        // act & assert
+        assertEq(lLimit.next(), 0);
+    }
+
+    function testNext_GreaterThanBufferSize(uint16 aStartingIndex) external {
+        // assume
+        uint16 lStartingIndex = uint16(bound(aStartingIndex, Buffer.SIZE, type(uint16).max));
+
+        // act & assert
+        unchecked {
+            assertEq(lStartingIndex.next(), (lStartingIndex + 1) % Buffer.SIZE);
+        }
+        assertLt(lStartingIndex.next(), Buffer.SIZE); // index returned always within bounds of Buffer.SIZE
+    }
+
+    function testAdd_IndexGreaterThanBufferSize(uint16 aStartingIndex, uint16 aOffset) external {
+        // assume
+        uint16 lStartingIndex = uint16(bound(aStartingIndex, Buffer.SIZE, type(uint16).max));
+
+        // act
+        uint16 lResult = lStartingIndex.add(aOffset);
+
+        // assert
+        assertLt(lResult, Buffer.SIZE);
+    }
+
+    function testSub_IndexGreaterThanBufferSize(uint16 aStartingIndex, uint16 aOffset) external {
+        // assume
+        uint16 lStartingIndex = uint16(bound(aStartingIndex, Buffer.SIZE, type(uint16).max));
+
+        // act
+        uint16 lResult = lStartingIndex.sub(aOffset);
+
+        // assert
+        assertLt(lResult, Buffer.SIZE);
+    }
+}