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: fixer.rs
    path of file: ./repos/ast-grep/crates/config/src
    
    the code of the file until where you have to start completion: use crate::maybe::Maybe;
use crate::rule::{Relation, Rule, RuleSerializeError, StopBy};
use crate::transform::Transformation;
use crate::DeserializeEnv;
use ast_grep_core::replacer::{Content, Replacer, TemplateFix, TemplateFixError};
use ast_grep_core::{Doc, Language, Matcher, NodeMatch};
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};
use thiserror::Error;

use std::collections::HashMap;
use std::ops::Range;

/// A pattern string or fix object to auto fix the issue.
/// It can reference metavariab
    
  fn test_parse_config() -> Result<(), FixerError> {
    let relation = from_str("{regex: ',', stopBy: neighbor}").expect("should deser");
    let config = SerializableFixConfig {
      expand_end: Maybe::Present(relation),
      expand_start: Maybe::Absent,
      template: "abcd".to_string(),
    };
    let config = SerializableFixer::Config(config);
    let env = DeserializeEnv::new(TypeScript::Tsx);
    let ret = Fixer::parse(&config, &env, &Some(Default::default()))?;
    assert!(ret.expand_start.is_none());
    assert!(ret.expand_end.is_some());
    assert!(matches!(ret.template, TemplateFix::Textual(_)));
    Ok(())
  }