Add tests for PreimageOracle (#6293)

packages/contracts-bedrock/.gas-snapshot

@@ -331,6 +331,9 @@ OptimismPortal_Test:test_receive_succeeds() (gas: 127513)
 OptimismPortal_Test:test_simple_isOutputFinalized_succeeds() (gas: 32971)
 OptimismPortal_Test:test_unpause_onlyGuardian_reverts() (gas: 46098)
 OptimismPortal_Test:test_unpause_succeeds() (gas: 31756)
+PreimageOracle_Test:test_computePreimageKey_succeeds() (gas: 6267)
+PreimageOracle_Test:test_loadKeccak256PreimagePart_outOfBoundsOffset_reverts() (gas: 9025)
+PreimageOracle_Test:test_loadKeccak256PreimagePart_succeeds() (gas: 77552)
 ProxyAdmin_Test:test_chugsplashChangeProxyAdmin_succeeds() (gas: 35586)
 ProxyAdmin_Test:test_chugsplashGetProxyAdmin_succeeds() (gas: 15675)
 ProxyAdmin_Test:test_chugsplashGetProxyImplementation_succeeds() (gas: 51084)

packages/contracts-bedrock/contracts/cannon/PreimageOracle.sol

 // SPDX-License-Identifier: MIT
-pragma solidity 0.8.15;
+pragma solidity ^0.8.15;
 
 /// @title PreimageOracle
 /// @notice A contract for storing permissioned pre-images.

packages/contracts-bedrock/contracts/test/PreimageOracle.t.sol

+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.15;
+
+import { Test } from "forge-std/Test.sol";
+
+import { PreimageOracle } from "../cannon/PreimageOracle.sol";
+
+contract PreimageOracle_Test is Test {
+    PreimageOracle oracle;
+
+    /// @notice Sets up the testing suite.
+    function setUp() public {
+        oracle = new PreimageOracle();
+        vm.label(address(oracle), "PreimageOracle");
+    }
+
+    /// @notice Test the pre-image key computation with a known pre-image.
+    function test_computePreimageKey_succeeds() public {
+        bytes memory preimage = hex"deadbeef";
+        bytes32 key = oracle.computePreimageKey(preimage);
+        bytes32 known = 0x02fd4e189132273036449fc9e11198c739161b4c0116a9a2dccdfa1c492006f1;
+        assertEq(key, known);
+    }
+
+    /// @notice Tests that a pre-image is correctly set.
+    function test_loadKeccak256PreimagePart_succeeds() public {
+        // Set the pre-image
+        bytes memory preimage = hex"deadbeef";
+        bytes32 key = oracle.computePreimageKey(preimage);
+        uint256 offset = 0;
+        oracle.loadKeccak256PreimagePart(offset, preimage);
+
+        // Validate the pre-image part
+        bytes32 part = oracle.preimageParts(key, offset);
+        bytes32 expectedPart = 0x0000000000000004deadbeef0000000000000000000000000000000000000000;
+        assertEq(part, expectedPart);
+
+        // Validate the pre-image length
+        uint256 length = oracle.preimageLengths(key);
+        assertEq(length, preimage.length);
+
+        // Validate that the pre-image part is set
+        bool ok = oracle.preimagePartOk(key, offset);
+        assertTrue(ok);
+    }
+
+    /// @notice Tests that a pre-image cannot be set with an out-of-bounds offset.
+    function test_loadKeccak256PreimagePart_outOfBoundsOffset_reverts() public {
+        bytes memory preimage = hex"deadbeef";
+        uint256 offset = preimage.length + 9;
+
+        vm.expectRevert();
+        oracle.loadKeccak256PreimagePart(offset, preimage);
+    }
+
+    /// @notice Reading a pre-image part that has not been set should revert.
+    function testFuzz_readPreimage_missingPreimage_reverts(bytes32 key, uint256 offset) public {
+        vm.expectRevert("pre-image must exist");
+        oracle.readPreimage(key, offset);
+    }
+}