diff --git a/approot.inc.php b/approot.inc.php
index 820ab0a6e..b4cbe59d6 100644
--- a/approot.inc.php
+++ b/approot.inc.php
@@ -25,4 +25,9 @@ define('ITOP_DESIGN_LATEST_VERSION', '3.1');
  */
 define('ITOP_CORE_VERSION', '3.1.0');
 
+/**
+ * @since 3.0.4 N°6274 Allow to test if PHPUnit is currently running. Starting with PHPUnit 9.5 we'll be able to replace it with $GLOBALS['phpunit_version']
+ */
+define('ITOP_PHPUNIT_RUNNING_CONSTANT_NAME', 'ITOP_PHPUNIT_RUNNING');
+
 require_once APPROOT.'bootstrap.inc.php';
diff --git a/core/log.class.inc.php b/core/log.class.inc.php
index a8ab6c41c..169bc72d9 100644
--- a/core/log.class.inc.php
+++ b/core/log.class.inc.php
@@ -1121,16 +1121,19 @@ class DeprecatedCallsLog extends LogAPI
 	 * @uses \set_error_handler() to catch deprecated notices
 	 *
 	 * @since 3.0.0 N°3002 logs deprecated notices in called code
+	 * @since 3.0.4 N°6274 do not set handler when in PHPUnit context (otherwise PHP notices won't be caught)
 	 */
-	public static function Enable($sTargetFile = null): void
-	{
+	public static function Enable($sTargetFile = null): void {
 		if (empty($sTargetFile)) {
 			$sTargetFile = APPROOT.'log/deprecated-calls.log';
 		}
 		parent::Enable($sTargetFile);
 
-		if (static::IsLogLevelEnabledSafe(self::LEVEL_WARNING, self::ENUM_CHANNEL_PHP_LIBMETHOD)) {
-			set_error_handler([static::class, 'DeprecatedNoticesErrorHandler']);
+		if (
+			(false === defined(ITOP_PHPUNIT_RUNNING_CONSTANT_NAME))
+			&& static::IsLogLevelEnabledSafe(self::LEVEL_WARNING, self::ENUM_CHANNEL_PHP_LIBMETHOD)
+		) {
+			set_error_handler([static::class, 'DeprecatedNoticesErrorHandler'], E_DEPRECATED | E_USER_DEPRECATED);
 		}
 	}
 
diff --git a/tests/php-unit-tests/ItopTestCase.php b/tests/php-unit-tests/ItopTestCase.php
index 0ac11233f..1a2b25db3 100644
--- a/tests/php-unit-tests/ItopTestCase.php
+++ b/tests/php-unit-tests/ItopTestCase.php
@@ -36,8 +36,7 @@ class ItopTestCase extends TestCase
 	static $DEBUG_UNIT_TEST = false;
 
 	/** @noinspection UsingInclusionOnceReturnValueInspection avoid errors for approot includes */
-	protected function setUp(): void
-	{
+	protected function setUp(): void {
 		$sAppRootRelPath = 'approot.inc.php';
 		$sDepthSeparator = '../';
 		for ($iDepth = 0; $iDepth < 8; $iDepth++) {
@@ -52,6 +51,11 @@ class ItopTestCase extends TestCase
 		static::$DEBUG_UNIT_TEST = getenv('DEBUG_UNIT_TEST');
 
 		$this->debug("\n----------\n---------- ".$this->getName()."\n----------\n");
+
+		if (false === defined(ITOP_PHPUNIT_RUNNING_CONSTANT_NAME)) {
+			// setUp might be called multiple times, so protecting the define() call !
+			define(ITOP_PHPUNIT_RUNNING_CONSTANT_NAME, true);
+		}
 	}
 
 	/**
diff --git a/tests/php-unit-tests/unitary-tests/core/Log/DeprecatedCallsLogTest.php b/tests/php-unit-tests/unitary-tests/core/Log/DeprecatedCallsLogTest.php
new file mode 100644
index 000000000..906246ff4
--- /dev/null
+++ b/tests/php-unit-tests/unitary-tests/core/Log/DeprecatedCallsLogTest.php
@@ -0,0 +1,61 @@
+<?php
+/*
+ * @copyright   Copyright (C) 2010-2023 Combodo SARL
+ * @license     http://opensource.org/licenses/AGPL-3.0
+ */
+
+namespace Combodo\iTop\Test\UnitTest\Core\Log;
+
+
+use Combodo\iTop\Test\UnitTest\ItopTestCase;
+use DeprecatedCallsLog;
+use PHPUnit\Framework\Error\Notice;
+use PHPUnit\Framework\Error\Warning;
+
+class DeprecatedCallsLogTest extends ItopTestCase {
+	/**
+	 * We are testing for a undefined offset error. This was throwing a Notice, but starting with PHP 8.0 it was converted to a Warning ! Also the message was changed :(
+	 *
+	 * @link https://www.php.net/manual/en/migration80.incompatible.php check "A number of notices have been converted into warnings:"
+	 */
+	private function SetUndefinedOffsetExceptionToExpect(): void {
+		if (version_compare(phpversion(), '8.0', '>=')) {
+			$sUndefinedOffsetExceptionClass = Warning::class;
+			$sUndefinedOffsetExceptionMessage = 'Undefined array key "tutu"';
+		}
+		else {
+			$sUndefinedOffsetExceptionClass = Notice::class;
+			$sUndefinedOffsetExceptionMessage = 'Undefined index: tutu';
+		}
+		$this->expectException($sUndefinedOffsetExceptionClass);
+		$this->expectExceptionMessage($sUndefinedOffsetExceptionMessage);
+	}
+
+	public function testPhpNoticeWithoutDeprecatedCallsLog(): void {
+		$this->SetUndefinedOffsetExceptionToExpect();
+
+		$aArray = [];
+		if ('toto' === $aArray['tutu']) {
+			//Do nothing, just raising a undefined offset warning
+		}
+	}
+
+	/**
+	 * The error handler set by DeprecatedCallsLog during startup was causing PHPUnit to miss PHP notices like "undefined offset"
+	 *
+	 * The error handler is now disabled when running PHPUnit
+	 *
+	 * @since 3.0.4 N°6274
+	 * @covers DeprecatedCallsLog::DeprecatedNoticesErrorHandler
+	 */
+	public function testPhpNoticeWithDeprecatedCallsLog(): void {
+		$this->RequireOnceItopFile('core/log.class.inc.php');
+		DeprecatedCallsLog::Enable(); // will set error handler
+		$this->SetUndefinedOffsetExceptionToExpect();
+
+		$aArray = [];
+		if ('toto' === $aArray['tutu']) {
+			//Do nothing, just raising a undefined offset warning
+		}
+	}
+}