Need Help using hook_views_query_filter
You shouldn't alter the query objects properties directly. You need to use the methods it provides. In this case, you need to use add_where(). I think you want to consider something like this:

&lt;?php
$clauses = array("field_test_value='%s'");
$args = array('test1');
$query-&gt;add_where(1, $clauses, $args);
$query-&gt;set_group_operator('OR'); // this is the operator that goes between WHERE groups
?&gt;