Add initial getPreviousOwnerInLinkedList tests

test/unit/SafeRecoverySubjectHandlerHarness.sol

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.25;
+
+import "forge-std/console2.sol";
+import { SafeRecoverySubjectHandler } from "src/handlers/SafeRecoverySubjectHandler.sol";
+
+contract SafeRecoverySubjectHandlerHarness is SafeRecoverySubjectHandler {
+    constructor() SafeRecoverySubjectHandler() { }
+
+    function exposed_getPreviousOwnerInLinkedList(
+        address safe,
+        address oldOwner
+    )
+        external
+        returns (address)
+    {
+        return getPreviousOwnerInLinkedList(safe, oldOwner);
+    }
+}

test/unit/SafeUnitBase.t.sol

@@ -27,14 +27,14 @@ import { Solarray } from "solarray/Solarray.sol";
 import { EmailRecoveryManagerHarness } from "./EmailRecoveryManagerHarness.sol";
 import { EmailRecoveryManager } from "src/EmailRecoveryManager.sol";
 import { EmailRecoveryModule } from "src/modules/EmailRecoveryModule.sol";
-import { SafeRecoverySubjectHandler } from "src/handlers/SafeRecoverySubjectHandler.sol";
+import { SafeRecoverySubjectHandlerHarness } from "./SafeRecoverySubjectHandlerHarness.sol";
 import { EmailRecoveryFactory } from "src/EmailRecoveryFactory.sol";
 import { MockRegistry } from "../integration/external/MockRegistry.sol";
 import { IntegrationBase } from "../integration/IntegrationBase.t.sol";
 
 abstract contract SafeUnitBase is IntegrationBase {
     EmailRecoveryFactory emailRecoveryFactory;
-    SafeRecoverySubjectHandler safeRecoverySubjectHandler;
+    SafeRecoverySubjectHandlerHarness safeRecoverySubjectHandler;
     EmailRecoveryManager emailRecoveryManager;
     address emailRecoveryManagerAddress;
     address recoveryModuleAddress;
@@ -60,7 +60,7 @@ abstract contract SafeUnitBase is IntegrationBase {
         super.setUp();
 
         // Deploy handler, manager and module
-        safeRecoverySubjectHandler = new SafeRecoverySubjectHandler();
+        safeRecoverySubjectHandler = new SafeRecoverySubjectHandlerHarness();
         emailRecoveryFactory = new EmailRecoveryFactory();
 
         emailRecoveryManager = new EmailRecoveryManagerHarness(

test/unit/handlers/SafeRecoverySubjectHandler/getPreviousOwnerInLinkedList.t.sol

@@ -5,12 +5,46 @@ import "forge-std/console2.sol";
 import { SafeUnitBase } from "../../SafeUnitBase.t.sol";
 
 contract SafeRecoverySubjectHandler_getPreviousOwnerInLinkedList_Test is SafeUnitBase {
+    address internal constant SENTINEL_OWNERS = address(0x1);
+
     function setUp() public override {
         super.setUp();
     }
 
-    function test_GetPreviousOwnerInLinkedList_RevertWhen_InvalidOldOwner() public view { }
-    function test_GetPreviousOwnerInLinkedList_RevertWhen_OldOwnerIsSentinel() public view { }
-    function test_GetPreviousOwnerInLinkedList_RevertWhen_OldOwnerIsZeroAddress() public view { }
-    function test_GetPreviousOwnerInLinkedList_Succeeds() public view { }
+    function test_GetPreviousOwnerInLinkedList_InvalidOwner_ReturnsSentinel() public {
+        address invalidOwner = address(0);
+
+        address previousOwner = safeRecoverySubjectHandler.exposed_getPreviousOwnerInLinkedList(
+            accountAddress, invalidOwner
+        );
+
+        assertEq(previousOwner, SENTINEL_OWNERS);
+    }
+
+    function test_GetPreviousOwnerInLinkedList_OwnerIsSentinel_ReturnsSentinel() public {
+        address invalidOwner = SENTINEL_OWNERS;
+
+        address previousOwner = safeRecoverySubjectHandler.exposed_getPreviousOwnerInLinkedList(
+            accountAddress, invalidOwner
+        );
+
+        assertEq(previousOwner, SENTINEL_OWNERS);
+    }
+
+    function test_GetPreviousOwnerInLinkedList_RevertWhen_InvalidAccount() public {
+        address invalidAccount = address(0);
+
+        vm.expectRevert();
+        safeRecoverySubjectHandler.exposed_getPreviousOwnerInLinkedList(invalidAccount, owner);
+    }
+
+    function test_GetPreviousOwnerInLinkedList_Succeeds() public {
+        address expectedPreviousOwner = address(1);
+        address previousOwner =
+            safeRecoverySubjectHandler.exposed_getPreviousOwnerInLinkedList(accountAddress, owner);
+
+        assertEq(expectedPreviousOwner, previousOwner);
+    }
+
+    function test_GetPreviousOwnerInLinkedList_SucceedsWithMultipleAccounts() public { }
 }