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: extremum.rs
    path of file: ./repos/readyset/readyset-dataflow/src/ops/grouped
    
    the code of the file until where you have to start completion: use readyset_data::DfType;
use readyset_errors::{invariant, ReadySetResult};
use serde::{Deserialize, Serialize};

use crate::node::AuxiliaryNodeState;
use crate::ops::grouped::{GroupedOperation, GroupedOperator};
use crate::prelude::*;

/// Supported kinds of extremum operators.
#[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq)]
pub enum Extremum {
    /// The minimum value that occurs in the `over` column in each group.
    Min,
    /// The maximum value of the `over` column for all records of each group.
    
    
    fn assert_record_change(group: i32, old: DfValue, new: DfValue, rs: Records) {
        assert_eq!(rs.len(), 2);
        let mut rs = rs.into_iter();

        match rs.next().unwrap() {
            Record::Negative(r) => {
                assert_eq!(r[0], group.into());
                assert_eq!(r[1], old);
            }
            _ => unreachable!(),
        }
        match rs.next().unwrap() {
            Record::Positive(r) => {
                assert_eq!(r[0], group.into());
                assert_eq!(r[1], new);
            }
            _ => unreachable!(),
        }
    }