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: ngram_tokenizer.rs
    path of file: ./repos/tantivy/src/tokenizer
    
    the code of the file until where you have to start completion: use super::{Token, TokenStream, Tokenizer};
use crate::TantivyError;

/// Tokenize the text by splitting words into n-grams of the given size(s)
///
/// With this tokenizer, the `position` is always 0.
/// Beware however, in presence of multiple value for the same fi
    
    fn test_utf8_codepoint_width() {
        // 0xxx
        for i in 0..128 {
            assert_eq!(utf8_codepoint_width(i), 1);
        }
        // 110xx
        for i in (128 | 64)..(128 | 64 | 32) {
            assert_eq!(utf8_codepoint_width(i), 2);
        }
        // 1110xx
        for i in (128 | 64 | 32)..(128 | 64 | 32 | 16) {
            assert_eq!(utf8_codepoint_width(i), 3);
        }
        // 1111xx
        for i in (128 | 64 | 32 | 16)..256 {
            assert_eq!(utf8_codepoint_width(i as u8), 4);
        }
    }