From b5d0ea36be27e6183c2bda8fc832123e5d9f8d1a Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Sun, 12 Apr 2026 19:49:28 -0700
Subject: [PATCH] [test] add `testResetInstance()` to simulate device reset
 (#12878)

This commit introduces `testResetInstance()` in the unit test platform
layer to finalize an existing `ot::Instance` and re-initialize it
using the same underlying memory buffer, simulating a device reset.

This commit also updates `test_routing_manager.cpp` to use this new
function to streamline the test implementation.
---
 tests/unit/test_platform.cpp        | 17 +++++++++++++++++
 tests/unit/test_platform.h          |  1 +
 tests/unit/test_routing_manager.cpp | 25 ++++++++++++-------------
 3 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/tests/unit/test_platform.cpp b/tests/unit/test_platform.cpp
index f74cbaf6c..055693af9 100644
--- a/tests/unit/test_platform.cpp
+++ b/tests/unit/test_platform.cpp
@@ -75,6 +75,23 @@ ot::Instance *testInitInstance(void)
     return static_cast<ot::Instance *>(instance);
 }
 
+ot::Instance *testResetInstance(ot::Instance *aInstance)
+{
+    otInstanceFinalize(aInstance);
+
+#if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
+    {
+        size_t instanceBufferLength = sizeof(ot::Instance);
+
+        aInstance = static_cast<ot::Instance *>(otInstanceInit(aInstance, &instanceBufferLength));
+    }
+#else
+    aInstance = static_cast<ot::Instance *>(otInstanceInitSingle());
+#endif
+
+    return aInstance;
+}
+
 #if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE && OPENTHREAD_CONFIG_MULTIPLE_STATIC_INSTANCE_ENABLE
 ot::Instance *testInitAdditionalInstance(uint8_t id)
 {
diff --git a/tests/unit/test_platform.h b/tests/unit/test_platform.h
index c72f7471e..4eedd4edc 100644
--- a/tests/unit/test_platform.h
+++ b/tests/unit/test_platform.h
@@ -51,6 +51,7 @@
 #include "test_util.h"
 
 ot::Instance *testInitInstance(void);
+ot::Instance *testResetInstance(ot::Instance *aInstance);
 #if OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE && OPENTHREAD_CONFIG_MULTIPLE_STATIC_INSTANCE_ENABLE
 ot::Instance *testInitAdditionalInstance(uint8_t id);
 #endif
diff --git a/tests/unit/test_routing_manager.cpp b/tests/unit/test_routing_manager.cpp
index d0e9801b3..e14a9ad1c 100644
--- a/tests/unit/test_routing_manager.cpp
+++ b/tests/unit/test_routing_manager.cpp
@@ -1386,19 +1386,23 @@ void VerifyFavoredOnLinkPrefix(const Ip6::Prefix &aPrefix)
     VerifyOrQuit(favoredPrefix == aPrefix);
 }
 
-void InitTest(bool aEnablBorderRouting = false, bool aAfterReset = false)
+void InitTest(bool aEnablBorderRouting = false, bool aResetInstance = false)
 {
     uint32_t delay = 10000;
 
     //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     // Initialize OT instance.
 
-    sNow      = 0;
-    sAlarmOn  = false;
-    sInstance = static_cast<Instance *>(testInitInstance());
+    sNow     = 0;
+    sAlarmOn = false;
 
-    if (aAfterReset)
+    if (!aResetInstance)
     {
+        sInstance = testInitInstance();
+    }
+    else
+    {
+        sInstance = testResetInstance(sInstance);
         delay += 26000; // leader reset sync delay
     }
 
@@ -4285,9 +4289,7 @@ void TestSavedOnLinkPrefixes(void)
 
     Log("Disabling and re-enabling OT Instance");
 
-    testFreeInstance(sInstance);
-
-    InitTest(/* aEnablBorderRouting */ true, /* aAfterReset */ true);
+    InitTest(/* aEnablBorderRouting */ true, /* aResetInstance */ true);
 
     sExpectedPio = kPioAdvertisingLocalOnLink;
 
@@ -4331,9 +4333,7 @@ void TestSavedOnLinkPrefixes(void)
 
     Log("Disabling and re-enabling OT Instance");
 
-    testFreeInstance(sInstance);
-
-    InitTest(/* aEnablBorderRouting */ false, /* aAfterReset */ true);
+    InitTest(/* aEnablBorderRouting */ false, /* aResetInstance */ true);
 
     //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     // Start Routing Manager.
@@ -4381,8 +4381,7 @@ void TestSavedOnLinkPrefixes(void)
 
     Log("Disabling and re-enabling OT Instance again");
 
-    testFreeInstance(sInstance);
-    InitTest(/* aEnablBorderRouting */ false, /* aAfterReset */ true);
+    InitTest(/* aEnablBorderRouting */ false, /* aResetInstance */ true);
 
     SuccessOrQuit(sInstance->Get<BorderRouter::RoutingManager>().SetEnabled(true));
     AdvanceTime(100);