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: string.rs
    path of file: ./repos/OctoBase/libs/jwst-codec/src/codec
    
    the code of the file until where you have to start completion: use std::io::{Error, Write};

us
    
    fn test_read_var_string() {
        // Test case 1: valid input, string length = 5
        let input = [0x05, 0x68, 0x65, 0x6C, 0x6C, 0x6F];
        let expected_output = "hello".to_string();
        let result = read_var_string(&input);
        assert_eq!(result, Ok((&[][..], expected_output)));

        // Test case 2: missing string length
        let input = [0x68, 0x65, 0x6C, 0x6C, 0x6F];
        let result = read_var_string(&input);
        assert_eq!(result, Err(Err::Error(Error::new(&input[1..], ErrorKind::Eof))));

        // Test case 3: truncated input
        let input = [0x05, 0x68, 0x65, 0x6C, 0x6C];
        let result = read_var_string(&input);
        assert_eq!(result, Err(Err::Error(Error::new(&input[1..], ErrorKind::Eof))));

        // Test case 4: invalid input
        let input = [0xFF, 0x01, 0x02, 0x03, 0x04];
        let result = read_var_string(&input);
        assert_eq!(result, Err(Err::Error(Error::new(&input[2..], ErrorKind::Eof))));

        // Test case 5: invalid var int encoding
        let input = [0xFF, 0x80, 0x80, 0x80, 0x80, 0x80, 0x01];
        let result = read_var_string(&input);
        assert_eq!(result, Err(Err::Error(Error::new(&input[7..], ErrorKind::Eof))));

        // Test case 6: invalid input, invalid UTF-8 encoding
        let input = [0x05, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF];
        let result = read_var_string(&input);
        assert_eq!(result, Err(Err::Error(Error::new(&input[..], ErrorKind::MapRes))));
    }