diff --git a/tests/php-unit-tests/unitary-tests/core/DBUnionSearchTest.php b/tests/php-unit-tests/unitary-tests/core/DBUnionSearchTest.php
new file mode 100644
index 000000000..ba2e6c565
--- /dev/null
+++ b/tests/php-unit-tests/unitary-tests/core/DBUnionSearchTest.php
@@ -0,0 +1,66 @@
+<?php
+/*
+ * @copyright   Copyright (C) 2010-2023 Combodo SARL
+ * @license     http://opensource.org/licenses/AGPL-3.0
+ */
+
+
+use Combodo\iTop\Test\UnitTest\ItopDataTestCase;
+
+/**
+ * @runTestsInSeparateProcesses
+ * @preserveGlobalState disabled
+ * @backupGlobals disabled
+ */
+class DBUnionSearchTest extends ItopDataTestCase
+{
+
+	public function testFilterOnFirstSelectedClass()
+	{
+		$sSourceOQL = 'SELECT `Person`, `Location` FROM Person AS `Person` JOIN Location AS `Location` ON `Person`.location_id = `Location`.id WHERE 1';
+		$oSearch = DBSearch::FromOQL($sSourceOQL);
+
+		$sFilterOQL = 'SELECT `Person` FROM Person AS `Person` WHERE (`Person`.`id` = 1) UNION SELECT `Person` FROM Person AS `Person` WHERE (`Person`.`id` = 1)';
+		$oVisibleObjects = DBSearch::FromOQL($sFilterOQL);
+		$sClassAlias = 'Person';
+		$oVisibleObjects->AllowAllData();
+		$oSearch = $oSearch->Filter($sClassAlias, $oVisibleObjects);
+		$this->InvokeNonPublicMethod(get_class($oSearch), 'SetDataFiltered', $oSearch, []);
+
+		$this->debug($oSearch->ToOQL());
+
+		$oSet = new DBObjectSet($oSearch);
+		$oSet->Count();
+
+		$this->assertTrue(true);
+	}
+
+	/**
+	 * Ignored test (provokes PHP Error)
+	 *
+	 * @return void
+	 * @throws \CoreException
+	 * @throws \MissingQueryArgument
+	 * @throws \MySQLException
+	 * @throws \MySQLHasGoneAwayException
+	 * @throws \OQLException
+	 */
+	public function FilterOnSecondSelectedClass()
+	{
+		$sSourceOQL = 'SELECT `Person`, `Location` FROM Person JOIN Location ON `Person`.location_id = `Location`.id';
+		$oSearch = DBSearch::FromOQL($sSourceOQL);
+
+		$sFilterOQL = 'SELECT Location UNION SELECT Location';
+		$oVisibleObjects = DBSearch::FromOQL($sFilterOQL);
+		$sClassAlias = 'Location';
+		$oVisibleObjects->AllowAllData();
+		$oSearch = $oSearch->Filter($sClassAlias, $oVisibleObjects);
+
+		// $oSearch->ToOQL();
+
+		$oSet = new DBObjectSet($oSearch);
+		$oSet->CountWithLimit(1);
+
+		$this->assertTrue(true);
+	}
+}