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: mod.rs
    path of file: ./repos/linfa/algorithms/linfa-preprocessing/src/countgrams
    
    the code of the file until where you have to start completion: //! Count vectorization methods

use std::collections::{HashMap, HashSet};
use std::io::Read;
use std::iter::IntoIterator;

use encoding::types::EncodingRef;
use encoding::DecoderTrap;
use ndarray::{Array1, ArrayBase, ArrayViewMut1, Data, Ix1};
use regex::Regex;
use sprs::{CsMat, CsVec};
use unicode_normalization::UnicodeNormalization;

use crate::error::{PreprocessingError, Result};
use crate::helpers::NGramList;
pub use hyperparams::{CountVectorizerParams, CountVectorizerValidParams};
use linfa::ParamGuard;

#[cfg(feature = "serde")]
use serde_crate::{Deserialize, Seri
    
    fn simple_count_no_punctuation_test() {
        let texts = array!["oNe two three four", "TWO three four", "three;four", "four"];
        let vectorizer = CountVectorizer::params()
            .split_regex(r"\b[^ ][^ ]+\b")
            .fit(&texts)
            .unwrap();
        let vocabulary = vectorizer.vocabulary();
        let counts: Array2<usize> = vectorizer.transform(&texts).to_dense();
        let true_vocabulary = vec!["one", "two", "three", "four", "three;four"];
        assert_vocabulary_eq(&true_vocabulary, vocabulary);
        assert_counts_for_word!(
            vocabulary,
            counts,
            ("one", array![1, 0, 0, 0]),
            ("two", array![1, 1, 0, 0]),
            ("three", array![1, 1, 0, 0]),
            ("four", array![1, 1, 0, 1]),
            ("three;four", array![0, 0, 1, 0])
        );
    }