diff --git a/src/extensions/extension_manager/tests/CMakeLists.txt b/src/extensions/extension_manager/tests/CMakeLists.txt
index 7fe6392a0..34cce0698 100644
--- a/src/extensions/extension_manager/tests/CMakeLists.txt
+++ b/src/extensions/extension_manager/tests/CMakeLists.txt
@@ -40,7 +40,12 @@ endif ()
 
 target_link_libraries (${target_name} PRIVATE libaducpal)
 
-target_compile_definitions (${target_name} PRIVATE ADUC_TEST_DATA_FOLDER="${ADUC_TEST_DATA_FOLDER}")
+target_compile_definitions (
+    ${target_name}
+    PRIVATE
+        ADUC_TEST_DATA_FOLDER="${ADUC_TEST_DATA_FOLDER}"
+        ADUC_CONTENT_DOWNLOADER_EXTENSION_PATH="${ADUC_EXTENSIONS_FOLDER}/${ADUC_EXTENSIONS_SUBDIR_CONTENT_DOWNLOADER}/${ADUC_EXTENSION_REG_FILENAME}"
+        ADUC_COMPONENT_ENUMERATOR_EXTENSION_PATH="${ADUC_EXTENSIONS_FOLDER}/${ADUC_EXTENSIONS_SUBDIR_COMPONENT_ENUMERATOR}/${ADUC_EXTENSION_REG_FILENAME}")
 
 include (CTest)
 include (Catch)
diff --git a/src/extensions/extension_manager/tests/src/extension_manager_helper_ut.cpp b/src/extensions/extension_manager/tests/src/extension_manager_helper_ut.cpp
index 59e5f30aa..7fb7319eb 100644
--- a/src/extensions/extension_manager/tests/src/extension_manager_helper_ut.cpp
+++ b/src/extensions/extension_manager/tests/src/extension_manager_helper_ut.cpp
@@ -6,6 +6,7 @@
  * Licensed under the MIT License.
  */
 
+#include <aduc/config_utils.h>
 #include <aduc/extension_manager_download_options.h>
 #include <aduc/extension_manager_helper.hpp>
 #include <aduc/result.h>
@@ -13,7 +14,59 @@
 
 #include <catch2/catch_all.hpp>
 
+#include <cstdlib> // setenv, getenv
 #include <cstring> // memset
+#include <string>
+
+namespace
+{
+
+// RAII guard that forces ADUC_ConfigInfo_GetInstance() to return nullptr by
+// temporarily pointing the config folder env var at a non-existent directory
+// and draining any existing singleton refcount.
+struct ScopedInvalidateConfig
+{
+    std::string savedEnv;
+    bool hadEnv = false;
+
+    ScopedInvalidateConfig()
+    {
+        const char* env = getenv("ADUC_CONF_FOLDER");
+        if (env != nullptr)
+        {
+            hadEnv = true;
+            savedEnv = env;
+        }
+        // Drain any existing singleton so re-init is attempted next time
+        // (ReleaseInstance is a no-op once refCount reaches 0).
+        const ADUC_ConfigInfo* cfg = ADUC_ConfigInfo_GetInstance();
+        if (cfg != nullptr)
+        {
+            // Release the ref we just took
+            ADUC_ConfigInfo_ReleaseInstance(cfg);
+            // Release again to drop refcount to 0 and uninit the singleton
+            ADUC_ConfigInfo_ReleaseInstance(cfg);
+        }
+        setenv("ADUC_CONF_FOLDER", "/nonexistent_path_for_test", 1);
+    }
+
+    ~ScopedInvalidateConfig()
+    {
+        if (hadEnv)
+        {
+            setenv("ADUC_CONF_FOLDER", savedEnv.c_str(), 1);
+        }
+        else
+        {
+            unsetenv("ADUC_CONF_FOLDER");
+        }
+    }
+
+    ScopedInvalidateConfig(const ScopedInvalidateConfig&) = delete;
+    ScopedInvalidateConfig& operator=(const ScopedInvalidateConfig&) = delete;
+};
+
+} // namespace
 
 // =====================================================================
 // ProcessDownloadHandlerExtensibility - Bad argument tests
@@ -130,15 +183,14 @@ TEST_CASE("GetDownloadTimeoutInMinutes returns default when downloadOptions is n
 
 TEST_CASE("GetDownloadTimeoutInMinutes returns downloadOptions value when config has zero timeout")
 {
+    ScopedInvalidateConfig noConfig;
     ExtensionManager_Download_Options options{};
     options.timeoutInMinutes = 42;
 
     unsigned int timeout = GetDownloadTimeoutInMinutes(&options);
 
-    // When config singleton is not initialized, it falls through to the
-    // downloadOptions path but config is nullptr so we get default.
-    // The config singleton returns nullptr if not initialized, so we
-    // get the default value.
+    // Config singleton is not initialized (env points to invalid path),
+    // so the function returns the default.
     CHECK(timeout == CONTENT_DOWNLOADER_MAX_TIMEOUT_IN_MINUTES_DEFAULT);
 }
 
@@ -166,6 +218,7 @@ TEST_CASE("Default_ExtensionManager_Download_Options has default timeout")
 
 TEST_CASE("GetDownloadTimeoutInMinutes returns default when downloadOptions has zero timeout")
 {
+    ScopedInvalidateConfig noConfig;
     ExtensionManager_Download_Options options{};
     options.timeoutInMinutes = 0;
 
@@ -177,6 +230,7 @@ TEST_CASE("GetDownloadTimeoutInMinutes returns default when downloadOptions has
 
 TEST_CASE("GetDownloadTimeoutInMinutes returns default for large timeout value in options")
 {
+    ScopedInvalidateConfig noConfig;
     ExtensionManager_Download_Options options{};
     options.timeoutInMinutes = 99999;
 
@@ -188,6 +242,7 @@ TEST_CASE("GetDownloadTimeoutInMinutes returns default for large timeout value i
 
 TEST_CASE("Default_ExtensionManager_Download_Options can be modified and used")
 {
+    ScopedInvalidateConfig noConfig;
     ExtensionManager_Download_Options opts = Default_ExtensionManager_Download_Options;
     opts.timeoutInMinutes = 120;
 
diff --git a/src/extensions/extension_manager/tests/src/extension_manager_ut.cpp b/src/extensions/extension_manager/tests/src/extension_manager_ut.cpp
index 0e26e415e..f1cbb27e1 100644
--- a/src/extensions/extension_manager/tests/src/extension_manager_ut.cpp
+++ b/src/extensions/extension_manager/tests/src/extension_manager_ut.cpp
@@ -20,6 +20,7 @@
 #include <aduc/calloc_wrapper.hpp>
 #include <aduc/workflow_internal.h>
 #include <aduc/workflow_utils.h>
+#include <cstdio> // std::rename
 #include <fstream>
 #include <memory>
 #include <parson.h>
@@ -59,6 +60,33 @@ struct ExtMgrCleanup
     }
 };
 
+// RAII guard that temporarily hides a file by renaming it so that
+// tests do not accidentally pick up real extension registrations
+// installed on the host (e.g. /var/lib/adu/extensions/…/extension.json).
+struct ScopedHideFile
+{
+    std::string original;
+    std::string hidden;
+    bool renamed = false;
+
+    explicit ScopedHideFile(const std::string& path)
+        : original(path), hidden(path + ".hidden_by_test")
+    {
+        renamed = (std::rename(original.c_str(), hidden.c_str()) == 0);
+    }
+
+    ~ScopedHideFile()
+    {
+        if (renamed)
+        {
+            std::rename(hidden.c_str(), original.c_str());
+        }
+    }
+
+    ScopedHideFile(const ScopedHideFile&) = delete;
+    ScopedHideFile& operator=(const ScopedHideFile&) = delete;
+};
+
 } // namespace
 
 // =====================================================================
@@ -417,6 +445,7 @@ TEST_CASE("LoadContentDownloaderLibrary returns cached downloader")
 TEST_CASE("LoadContentDownloaderLibrary fails when extension load fails and no cached")
 {
     ExtMgrCleanup cleanup;
+    ScopedHideFile hideExtJson(ADUC_CONTENT_DOWNLOADER_EXTENSION_PATH);
     ExtensionManager::SetContentDownloaderLibrary(nullptr);
 
     void* lib = nullptr;
@@ -431,6 +460,7 @@ TEST_CASE("LoadContentDownloaderLibrary fails when extension load fails and no c
 TEST_CASE("IsComponentsEnumeratorRegistered returns false when no enumerator loaded")
 {
     ExtMgrCleanup cleanup;
+    ScopedHideFile hideExtJson(ADUC_COMPONENT_ENUMERATOR_EXTENSION_PATH);
     bool registered = ExtensionManager::IsComponentsEnumeratorRegistered();
     CHECK_FALSE(registered);
 }
@@ -442,6 +472,7 @@ TEST_CASE("IsComponentsEnumeratorRegistered returns false when no enumerator loa
 TEST_CASE("LoadComponentEnumeratorLibrary fails when extension not found")
 {
     ExtMgrCleanup cleanup;
+    ScopedHideFile hideExtJson(ADUC_COMPONENT_ENUMERATOR_EXTENSION_PATH);
     void* lib = nullptr;
     ADUC_Result result = ExtensionManager::LoadComponentEnumeratorLibrary(&lib);
     CHECK(result.ResultCode == 0);
@@ -454,6 +485,7 @@ TEST_CASE("LoadComponentEnumeratorLibrary fails when extension not found")
 TEST_CASE("InitializeContentDownloader fails when downloader lib not loaded")
 {
     ExtMgrCleanup cleanup;
+    ScopedHideFile hideExtJson(ADUC_CONTENT_DOWNLOADER_EXTENSION_PATH);
     ExtensionManager::SetContentDownloaderLibrary(nullptr);
 
     ADUC_Result result = ExtensionManager::InitializeContentDownloader("test", ADUC_LOG_DEBUG);
@@ -481,6 +513,7 @@ TEST_CASE("InitializeContentDownloader fails when contract version is unsupporte
 TEST_CASE("GetAllComponents fails when component enumerator not loadable")
 {
     ExtMgrCleanup cleanup;
+    ScopedHideFile hideExtJson(ADUC_COMPONENT_ENUMERATOR_EXTENSION_PATH);
     std::string output;
     ADUC_Result result = ExtensionManager::GetAllComponents(output);
     CHECK(result.ResultCode == 0);
@@ -490,6 +523,7 @@ TEST_CASE("GetAllComponents fails when component enumerator not loadable")
 TEST_CASE("SelectComponents fails when component enumerator not loadable")
 {
     ExtMgrCleanup cleanup;
+    ScopedHideFile hideExtJson(ADUC_COMPONENT_ENUMERATOR_EXTENSION_PATH);
     std::string output;
     ADUC_Result result = ExtensionManager::SelectComponents("{}", output);
     CHECK(result.ResultCode == 0);
@@ -508,6 +542,7 @@ TEST_CASE("ExtensionManager_Uninit wraps Uninit")
 TEST_CASE("ExtensionManager_InitializeContentDownloader wrapper returns failure when no downloader")
 {
     ExtMgrCleanup cleanup;
+    ScopedHideFile hideExtJson(ADUC_CONTENT_DOWNLOADER_EXTENSION_PATH);
     ExtensionManager::SetContentDownloaderLibrary(nullptr);
 
     ADUC_Result result = ExtensionManager_InitializeContentDownloader("test", ADUC_LOG_DEBUG);
@@ -761,6 +796,7 @@ TEST_CASE("Download returns hash-type-not-supported when entity has no hashes")
 TEST_CASE("ExtensionManager_Download C wrapper fails when no downloader library loaded")
 {
     ExtMgrCleanup cleanup;
+    ScopedHideFile hideExtJson(ADUC_CONTENT_DOWNLOADER_EXTENSION_PATH);
     ExtensionManager::SetContentDownloaderLibrary(nullptr);
 
     const std::string testWorkfolder = std::string{ ADUC_TEST_DATA_FOLDER } + "/extension_manager";