If you want to use just fraction you can use:

const { fraction } = require("mathjs");

//In your test
fraction(oddsValue);

If you want to use others as well, you can do:

import { create, all } from "mathjs"
const math = create(all, {})

//In your test
math.fraction(oddsValue)

The mathjs has no default export, so you import everything (*) and then name it in your import

import * as math from 'mathjs'

This is the main entry point for the mathjs package.

// configuration
export { config } from './configReadonly.js'

// functions and constants
export * from './pureFunctionsAny.generated.js'
export * from './impureFunctionsAny.generated.js'
export * from './typeChecks.js'

// error classes
export { IndexError } from '../error/IndexError.js'
export { DimensionError } from '../error/DimensionError.js'
export { ArgumentsError } from '../error/ArgumentsError.js'

// dependency groups
export * from './dependenciesAny.generated.js'

// factory functions
export * from '../factoriesAny.js'

// core
export { create } from '../core/create.js'
export { factory } from '../utils/factory.js'

If it had a default export, there would be

export default {
  function1,
  function2,
  function3,
  ...
}

and then you can import it without using * as math.