Add pausable ism (#2675)

solidity/contracts/isms/PausableIsm.sol

@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+pragma solidity >=0.8.0;
+
+// ============ External Imports ============
+import {Pausable} from "@openzeppelin/contracts/security/Pausable.sol";
+import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
+
+// ============ Internal Imports ============
+import {IInterchainSecurityModule} from "../interfaces/IInterchainSecurityModule.sol";
+
+contract PausableIsm is IInterchainSecurityModule, Ownable, Pausable {
+    uint8 public constant override moduleType = uint8(Types.NULL);
+
+    /**
+     * @inheritdoc IInterchainSecurityModule
+     * @dev Reverts when paused, otherwise returns `true`.
+     */
+    function verify(bytes calldata, bytes calldata)
+        external
+        view
+        whenNotPaused
+        returns (bool)
+    {
+        return true;
+    }
+
+    function pause() external onlyOwner {
+        _pause();
+    }
+
+    function unpause() external onlyOwner {
+        _unpause();
+    }
+}

solidity/test/isms/PausableIsm.t.sol

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: MIT or Apache-2.0
+pragma solidity ^0.8.13;
+
+import {Test} from "forge-std/Test.sol";
+
+import {PausableIsm} from "../../contracts/isms/PausableIsm.sol";
+
+contract PausableIsmTest is Test {
+    PausableIsm ism;
+
+    function setUp() public {
+        ism = new PausableIsm();
+    }
+
+    function test_verify() public {
+        assertTrue(ism.verify("", ""));
+        ism.pause();
+        vm.expectRevert(bytes("Pausable: paused"));
+        ism.verify("", "");
+    }
+
+    function test_pause() public {
+        ism.pause();
+        assertTrue(ism.paused());
+    }
+
+    function test_unpause() public {
+        ism.pause();
+        ism.unpause();
+        assertFalse(ism.paused());
+    }
+}