test: add ErrantryRegistrationTest for client registration functionality

contracts/test/ErrantryRegistration.t.sol

@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.28;
+
+import {IEntryPoint} from "@account-abstraction/contracts/interfaces/IEntryPoint.sol";
+import {IErrantry} from "../src/interfaces/IErrantry.sol";
+import {Errantry} from "../src/Errantry.sol";
+import {MockEntryPoint} from "./mocks/MockEntryPoint.sol";
+import "forge-std/Test.sol";
+
+contract ErrantryRegistrationTest is Test {
+    // Contracts
+    Errantry private errantry;
+    MockEntryPoint private mockEntryPoint;
+
+    // Addresses
+    address private oracle = address(0xACE0); // pretend this is your trusted oracle
+    address private alice = address(0xA11CE);
+    address private bob = address(0xB0B);
+
+    function setUp() public {
+        // Deploy a mock EntryPoint
+        mockEntryPoint = new MockEntryPoint();
+
+        // Deploy Errantry with the mock entry point + set `oracle`
+        errantry = new Errantry(IEntryPoint(address(mockEntryPoint)), oracle);
+    }
+
+    function testRegisterNewClient_Success() public {
+        // By default, msg.sender in Foundry is address(this), so we can prank to simulate calls
+        vm.prank(alice);
+        errantry.registerNewClient(alice); // or pass some other param if your design changed
+
+        bool isRegistered = errantry.isClientRegistered(alice);
+        assertTrue(isRegistered, "Client should be registered");
+    }
+
+    function testRegisterNewClient_FailsIfAlreadyRegistered() public {
+        // Register once
+        vm.prank(alice);
+        errantry.registerNewClient(alice);
+
+        // Try registering again
+        vm.startPrank(alice);
+        vm.expectRevert(IErrantry.ClientAlreadyRegistered.selector);
+        errantry.registerNewClient(alice);
+        vm.stopPrank();
+    }
+
+    function testIsClientRegistered_ReturnsFalseIfNotRegistered() public view {
+        bool isRegistered = errantry.isClientRegistered(bob);
+        assertFalse(isRegistered, "Client should not be registered yet");
+    }
+}