I got it. I have to check, if in array is "['meta_query'][0]['value']" set or not :)
add_filter('rest_test_query', function($args) {
$args['meta_query'] = array(
array(
'key' => 'test_1',
'value' => esc_sql( $_GET['test_1'] ),
)
);
//echo $args['meta_query'][0]['value'];
//print_r($args);
if (!empty($args['meta_query'][0]['value'])) {
return $args;
}
} );