You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: opt.rs
    path of file: ./repos/pest/derive/tests
    
    the code of the file until where you have to start completion: // Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. All files in the project carrying such notice may not be copied,
// modified, or distributed except according to those terms.

#![cfg_attr(not(feature = "std"), no_std)]
extern crate alloc;
extern crate pest;
extern crate pest_derive;

#[cfg(feature = "grammar-extras")]
use pe
    
fn test_opt_tag() {
    let successful_parse = TestOptParser::parse(Rule::expr, "*");
    assert!(successful_parse.is_ok());
    let pairs = successful_parse.unwrap();
    assert!(pairs.find_first_tagged("prefix").is_some());
    assert!(pairs.find_first_tagged("suffix").is_none());

    // Test with no STAR or DOT
    let parse_no_components = TestOptParser::parse(Rule::expr, "");
    assert!(parse_no_components.is_ok());
    let pairs_no_components = parse_no_components.unwrap();
    assert!(pairs_no_components.find_first_tagged("prefix").is_none());
    assert!(pairs_no_components.find_first_tagged("suffix").is_none());

    // Test with only DOT
    let parse_only_dot = TestOptParser::parse(Rule::expr, ".");
    assert!(parse_only_dot.is_ok());
    let pairs_only_dot = parse_only_dot.unwrap();
    assert!(pairs_only_dot.find_first_tagged("prefix").is_none());
    assert!(pairs_only_dot.find_first_tagged("suffix").is_some());
}