Update QueryBuilderTest.php

Add test for UNION/UNION ALL function.
It could be useful to use "phpunit --group=db --filter testBuildUnion" command for run it.

tests/unit/framework/db/QueryBuilderTest.php

@@ -215,4 +215,30 @@ class QueryBuilderTest extends DatabaseTestCase
 		$this->assertEquals($expectedQueryParams, $queryParams);
 	}
 	*/
+	
+	/*
+	This test contains three select queries connected with UNION and UNION ALL constructions.
+	It could be useful to use "phpunit --group=db --filter testBuildUnion" command for run it.
+	*/
+	 public function testBuildUnion()
+	 {
+	 	$expectedQuerySql = "SELECT `id` FROM `TotalExample` `t1` WHERE (w > 0) AND (x < 2) UNION ( SELECT `id` FROM `TotalTotalExample` `t2` WHERE w > 5 ) UNION ALL ( SELECT `id` FROM `TotalTotalExample` `t3` WHERE w = 3 )";
+    		$query = new Query();
+    		$secondQuery = new Query();
+    		$secondQuery->select('id')
+      			->from('TotalTotalExample t2')
+      			->where('w > 5');
+    		$thirdQuery = new Query();
+    		$thirdQuery->select('id')
+      			->from('TotalTotalExample t3')
+      			->where('w = 3');
+    		$query->select('id')
+      			->from('TotalExample t1')
+      			->where(['and', 'w > 0', 'x < 2'])
+      			->union($secondQuery)
+      			->union($thirdQuery, TRUE);
+    		list($actualQuerySql, $queryParams) = $this->getQueryBuilder()->build($query);
+    		$this->assertEquals($expectedQuerySql, $actualQuerySql);
+  	 }
+
 }