diff --git a/core/metamodel.class.php b/core/metamodel.class.php
index 60afe675f..7b7143a42 100644
--- a/core/metamodel.class.php
+++ b/core/metamodel.class.php
@@ -7627,14 +7627,12 @@ abstract class MetaModel
 		// Build the list of available extensions
 		//
 		$aInterfaces = [
-			'iApplicationUIExtension',
-			'iPreferencesExtension',
-			'iApplicationObjectExtension',
 			'iLoginFSMExtension',
-			'iLoginUIExtension',
 			'iLogoutExtension',
-			'iQueryModifier',
-			'iOnClassInitialization',
+			'iLoginUIExtension',
+			'iPreferencesExtension',
+			'iApplicationUIExtension',
+			'iApplicationObjectExtension',
 			'iPopupMenuExtension',
 			'iPageUIExtension',
 			'iPageUIBlockExtension',
@@ -7648,10 +7646,12 @@ abstract class MetaModel
 			'iBackofficeDictEntriesExtension',
 			'iBackofficeDictEntriesPrefixesExtension',
 			'iPortalUIExtension',
-			'ModuleHandlerApiInterface',
-			'iNewsroomProvider',
+			'iQueryModifier',
+			'iOnClassInitialization',
 			'iModuleExtension',
 			'iKPILoggerExtension',
+			'ModuleHandlerApiInterface',
+			'iNewsroomProvider',
 		];
 		foreach ($aInterfaces as $sInterface) {
 			self::$m_aExtensionClassNames[$sInterface] = array();
diff --git a/tests/php-unit-tests/phpunit.xml.dist b/tests/php-unit-tests/phpunit.xml.dist
index 419e26538..70b3ba593 100644
--- a/tests/php-unit-tests/phpunit.xml.dist
+++ b/tests/php-unit-tests/phpunit.xml.dist
@@ -19,6 +19,10 @@
         printerClass="\Sempro\PHPUnitPrettyPrinter\PrettyPrinterForPhpUnit9"
 >
 
+  <extensions>
+    <extension class="Combodo\iTop\Test\UnitTest\Hook\TestsRunStartHook" />
+  </extensions>
+
   <php>
     <ini name="memory_limit" value="512M"/>
     <ini name="error_reporting" value="E_ALL"/>
diff --git a/tests/php-unit-tests/postbuild_integration.xml.dist b/tests/php-unit-tests/postbuild_integration.xml.dist
index df0cee5e0..8cc2825cd 100644
--- a/tests/php-unit-tests/postbuild_integration.xml.dist
+++ b/tests/php-unit-tests/postbuild_integration.xml.dist
@@ -19,6 +19,10 @@
         printerClass="\Sempro\PHPUnitPrettyPrinter\PrettyPrinterForPhpUnit9"
 >
 
+  <extensions>
+    <extension class="Combodo\iTop\Test\UnitTest\Hook\TestsRunStartHook" />
+  </extensions>
+
     <php>
         <ini name="error_reporting" value="E_ALL"/>
         <ini name="display_errors" value="On"/>
diff --git a/tests/php-unit-tests/unitary-tests/application/applicationextension/ApplicationExtensionTest.php b/tests/php-unit-tests/unitary-tests/application/applicationextension/ApplicationExtensionTest.php
new file mode 100644
index 000000000..58dc826df
--- /dev/null
+++ b/tests/php-unit-tests/unitary-tests/application/applicationextension/ApplicationExtensionTest.php
@@ -0,0 +1,164 @@
+<?php
+/*
+ * @copyright   Copyright (C) 2010-2023 Combodo SARL
+ * @license     http://opensource.org/licenses/AGPL-3.0
+ */
+
+namespace Combodo\iTop\Test\UnitTest\Application;
+
+use Combodo\iTop\Test\UnitTest\ItopCustomDatamodelTestCase;
+use MetaModel;
+use utils;
+
+/**
+ * @covers \iBackofficeLinkedScriptsExtension
+ */
+class ApplicationExtensionTest extends ItopCustomDatamodelTestCase
+{
+	protected const ENUM_API_CALL_METHOD_ENUMPLUGINS = 'MetaModel::EnumPlugins';
+	protected const ENUM_API_CALL_METHOD_GETCLASSESFORINTERFACE = 'utils::GetClassesForInterface';
+
+	/**
+	 * @inheritDoc
+	 */
+	public function GetDatamodelDeltaAbsPath(): string
+	{
+		return __DIR__ . '/Delta/application-extension-usages-in-snippets.xml';
+	}
+
+	/**
+	 * This test ensures that APIs are discovered / registered / called.
+	 *
+	 * It was introduced after {@since N°6436} when some APIs registration in \MetaModel::InitClasses() were lost during a merge {@link https://github.com/Combodo/iTop/commit/6432678de9f635990e22a6512e5b30713c22204a#diff-c94890a26989b5a5ce638f82e8cc7d4c7aa24e6fbb9c2ca89850e8fa4e0e9adaL3004} preventing them from being called when requested. This was hard to detect as it needed an extension to use the lost API to witness that it was no longer called.
+	 *
+	 * For each new API, a new test case should be added here to ensure that we don't lose it later.
+	 * To do so:
+	 * - Add the API to the provider
+	 * - Add a class extending / implementing the API in ./Delta/application-extension-usages-in-snippets.xml
+	 *
+	 * @param string $sAPIFQCN
+	 * @param string $sCallMethod
+	 *
+	 * @return void
+	 * @dataProvider ExtensionAPIRegisteredAndCalledProvider
+	 */
+	public function testExtensionAPIRegisteredAndCalled(string $sAPIFQCN, string $sCallMethod)
+	{
+		if ($sCallMethod === static::ENUM_API_CALL_METHOD_ENUMPLUGINS) {
+			$iExtendingClassesCount = count(MetaModel::EnumPlugins($sAPIFQCN));
+		} else {
+			$iExtendingClassesCount = count(utils::GetClassesForInterface($sAPIFQCN, '', ['[\\\\/]lib[\\\\/]', '[\\\\/]node_modules[\\\\/]', '[\\\\/]test[\\\\/]', '[\\\\/]tests[\\\\/]']));
+		}
+		$this->assertGreaterThan(0, $iExtendingClassesCount, "Found no class extending the $sAPIFQCN API");
+	}
+
+	public function ExtensionAPIRegisteredAndCalledProvider(): array
+	{
+		// APIs not concerned by this test:
+		// * \iRestServiceProvider as it is discovered by iterating over declared classes directly
+		// * \iLoginUIExtension as it is not iterated directly, only its derived interfaces
+
+		return [
+			\iLoginFSMExtension::class => [
+				\iLoginFSMExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iLogoutExtension::class => [
+				\iLogoutExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iLoginUIExtension::class => [
+				\iLoginUIExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iPreferencesExtension::class => [
+				\iPreferencesExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iApplicationUIExtension::class => [
+				\iApplicationUIExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iApplicationObjectExtension::class => [
+				\iApplicationObjectExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iPopupMenuExtension::class => [
+				\iPopupMenuExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iPageUIExtension::class => [
+				\iPageUIExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iPageUIBlockExtension::class => [
+				\iPageUIBlockExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iBackofficeLinkedScriptsExtension::class => [
+				\iBackofficeLinkedScriptsExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iBackofficeEarlyScriptExtension::class => [
+				\iBackofficeEarlyScriptExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iBackofficeScriptExtension::class => [
+				\iBackofficeScriptExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iBackofficeInitScriptExtension::class => [
+				\iBackofficeInitScriptExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iBackofficeReadyScriptExtension::class => [
+				\iBackofficeReadyScriptExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iBackofficeLinkedStylesheetsExtension::class => [
+				\iBackofficeLinkedStylesheetsExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iBackofficeStyleExtension::class => [
+				\iBackofficeStyleExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iBackofficeDictEntriesExtension::class => [
+				\iBackofficeDictEntriesExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iBackofficeDictEntriesPrefixesExtension::class => [
+				\iBackofficeDictEntriesPrefixesExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iPortalUIExtension::class => [
+				\iPortalUIExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iQueryModifier::class => [
+				\iQueryModifier::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iOnClassInitialization::class => [
+				\iOnClassInitialization::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iModuleExtension::class => [
+				\iModuleExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iKPILoggerExtension::class => [
+				\iKPILoggerExtension::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\ModuleHandlerApiInterface::class => [
+				\ModuleHandlerApiInterface::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+			\iNewsroomProvider::class => [
+				\iNewsroomProvider::class,
+				static::ENUM_API_CALL_METHOD_ENUMPLUGINS,
+			],
+		];
+	}
+}
diff --git a/tests/php-unit-tests/unitary-tests/application/applicationextension/Delta/application-extension-usages-in-snippets.xml b/tests/php-unit-tests/unitary-tests/application/applicationextension/Delta/application-extension-usages-in-snippets.xml
new file mode 100644
index 000000000..edbae0d0d
--- /dev/null
+++ b/tests/php-unit-tests/unitary-tests/application/applicationextension/Delta/application-extension-usages-in-snippets.xml
@@ -0,0 +1,384 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<itop_design xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.7">
+  <snippets>
+    <!-- These snippets just implements application/applicationextension.inc.php APIs for the ApplicationExtensionTest unit test -->
+    <snippet id="ExampleFor_iLoginFSMExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iLoginFSMExtension extends \AbstractLoginFSMExtension
+{
+	public function ListSupportedLoginModes()
+	{
+		// Do nothing, we just need the class to exists for the unit test
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iLogoutExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iLogoutExtension implements \iLogoutExtension
+{
+	public function LogoutAction()
+	{
+		// Do nothing, we just need the class to exists for the unit test
+	}
+
+	public function ListSupportedLoginModes()
+	{
+		// Do nothing, we just need the class to exists for the unit test
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iLoginUIExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iLoginUIExtension implements \iLoginUIExtension
+{
+	public function GetTwigContext()
+	{
+		// Do nothing, we just need the class to exists for the unit test
+	}
+
+	public function ListSupportedLoginModes()
+	{
+		// Do nothing, we just need the class to exists for the unit test
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iPreferencesExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iPreferencesExtension extends \AbstractPreferencesExtension
+{
+	// Do nothing, we just need the class to exists for the unit test
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iApplicationUIExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iApplicationUIExtension extends \AbstractApplicationUIExtension
+{
+	// Do nothing, we just need the class to exists for the unit test
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iApplicationObjectExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iApplicationObjectExtension extends \AbstractApplicationObjectExtension
+{
+	// Do nothing, we just need the class to exists for the unit test
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iPopupMenuExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iPopupMenuExtension implements \iPopupMenuExtension
+{
+  public static function EnumItems($iMenuId, $param)
+  {
+	  // Do nothing, we just need the class to exists for the unit test
+  }
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_ApplicationPopupMenuItem" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_ApplicationPopupMenuItem extends \ApplicationPopupMenuItem
+{
+  public function GetMenuItem()
+  {
+	  // Do nothing, we just need the class to exists for the unit test
+  }
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iPageUIExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iPageUIExtension extends \AbstractPageUIExtension
+{
+	// Do nothing, we just need the class to exists for the unit test
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExamplePageUIBlockExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iPageUIBlockExtension extends \AbstractPageUIBlockExtension
+{
+	// Do nothing, we just need the class to exists for the unit test
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iBackofficeLinkedScriptsExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iBackofficeLinkedScriptsExtension implements \iBackofficeLinkedScriptsExtension
+{
+	public function GetLinkedScriptsAbsUrls(): array
+	{
+		return [
+			'https://foo.bar/first.js',
+			'https://foo.bar/second.js',
+		];
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iBackofficeEarlyScriptExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iBackofficeEarlyScriptExtension implements \iBackofficeEarlyScriptExtension
+{
+	public function GetEarlyScript(): string
+	{
+		return <<<JS
+console.log('This is a PHP unit test');
+JS;
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iBackofficeScriptExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iBackofficeScriptExtension implements \iBackofficeScriptExtension
+{
+	public function GetScript(): string
+	{
+		return <<<JS
+console.log('This is a PHP unit test');
+JS;
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iBackofficeInitScriptExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iBackofficeInitScriptExtension implements \iBackofficeInitScriptExtension
+{
+	public function GetInitScript(): string
+	{
+		return <<<JS
+console.log('This is a PHP unit test');
+JS;
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iBackofficeReadyScriptExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iBackofficeReadyScriptExtension implements \iBackofficeReadyScriptExtension
+{
+	public function GetReadyScript(): string
+	{
+		return <<<JS
+console.log('This is a PHP unit test');
+JS;
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iBackofficeLinkedStylesheetsExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iBackofficeLinkedStylesheetsExtension implements \iBackofficeLinkedStylesheetsExtension
+{
+	public function GetLinkedStylesheetsAbsUrls(): array
+	{
+		return [
+      'https://foo.bar/first.css',
+			'https://foo.bar/second.css',
+		];
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iBackofficeStyleExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iBackofficeStyleExtension implements \iBackofficeStyleExtension
+{
+	public function GetStyle(): string
+	{
+		return <<<CSS
+.foo {
+  color: inherit;
+}
+CSS;
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iBackofficeDictEntriesExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iBackofficeDictEntriesExtension implements \iBackofficeDictEntriesExtension
+{
+	public function GetDictEntries(): array
+	{
+		return [
+		  'Foo:First' => 'Foo is first',
+		  'Foo:Second' => 'Foo is second',
+		];
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iBackofficeDictEntriesPrefixesExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iBackofficeDictEntriesPrefixesExtension implements \iBackofficeDictEntriesPrefixesExtension
+{
+	public function GetDictEntriesPrefixes(): array
+	{
+		return [
+		  'Foo:',
+		  'Bar:',
+		];
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iPortalUIExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iPortalUIExtension extends \AbstractPortalUIExtension
+{
+	// Do nothing, we just need the class to exists for the unit test
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iQueryModifier" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iQueryModifier implements \iQueryModifier
+{
+	public function __construct()
+	{
+	  // Do nothing, we just need the class to exists for the unit test
+	}
+
+	public function GetFieldExpression(QueryBuilderContext &$oBuild, $sClass, $sAttCode, $sColId, Expression $oFieldSQLExp, SQLQuery &$oSelect)
+	{
+	  // Do nothing, we just need the class to exists for the unit test
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iOnClassInitialization" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iOnClassInitialization implements \iOnClassInitialization
+{
+	public function OnAfterClassInitialization($sClass)
+	{
+	  // Do nothing, we just need the class to exists for the unit test
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iModuleExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iModuleExtension implements \iModuleExtension
+{
+	public function __construct()
+	{
+	  // Do nothing, we just need the class to exists for the unit test
+	}
+}
+      ]]></content>
+    </snippet>
+    <snippet id="ExampleFor_iKPILoggerExtension" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iKPILoggerExtension implements \iKPILoggerExtension
+{
+	public function InitStats()
+	{
+		// Do nothing, we just need the class to exists for the unit test
+	}
+
+	public function LogOperation($oKpiLogData)
+	{
+	  // Do nothing, we just need the class to exists for the unit test
+	}
+}
+      ]]></content>
+    </snippet>
+    <!-- These snippets just implements core/modulehandler.class.inc.php APIs for the ApplicationExtensionTest unit test -->
+    <snippet id="ExampleFor_ModuleHandlerApiInterface" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_ModuleHandlerApiInterface extends \ModuleHandlerAPI
+{
+	// Do nothing, we just need the class to exists for the unit test
+}
+      ]]></content>
+    </snippet>
+    <!-- These snippets just implements application/newsroomprovider.class.inc.php APIs for the ApplicationExtensionTest unit test -->
+    <snippet id="ExampleFor_iNewsroomProvider" _delta="define">
+      <placement>core</placement>
+      <rank>0</rank>
+      <content><![CDATA[
+class ExampleFor_iNewsroomProvider extends \NewsroomProviderBase
+{
+	public function GetLabel()
+	{
+	  // Do nothing, we just need the class to exists for the unit test
+  }
+
+	public function GetFetchURL()
+	{
+	  // Do nothing, we just need the class to exists for the unit test
+  }
+
+	public function GetMarkAllAsReadURL()
+	{
+	  // Do nothing, we just need the class to exists for the unit test
+  }
+
+	public function GetViewAllURL()
+	{
+	  // Do nothing, we just need the class to exists for the unit test
+  }
+}
+      ]]></content>
+    </snippet>
+  </snippets>
+</itop_design>
\ No newline at end of file