public function test_filter_ref_array_result() {
    $obj = new stdClass();
    $a   = new MockAction();
    $b   = new MockAction();
    $tag = __FUNCTION__;

    add_action( $tag, array( $a, 'filter_append' ), 10, 2 );
    add_action( $tag, array( $b, 'filter_append' ), 10, 2 );

    $result = apply_filters_ref_array( $tag, array( 'string', &$obj ) );

    $this->assertSame( $result, 'string_append_append' );

    $args = $a->get_args();
    $this->assertSame( $args[0][1], $obj );
    // Just in case we don't trust assertSame().
    $obj->foo = true;
    $this->assertNotEmpty( $args[0][1]->foo );

    $args = $b->get_args();
    $this->assertSame( $args[0][1], $obj );
    // Just in case we don't trust assertSame().
    $obj->foo = true;
    $this->assertNotEmpty( $args[0][1]->foo );

  }