setName.js

import type {Person} from './types';

export default function setName(person: Person, name: string): Person {
  return {
    ...person,
    name
  };
}

setName.test.js

import setName from './setName';

require('jasmine-check').install();

describe('setName', () => {
  check.it('sets a new name', [setName.asGenerator()], (args) => {
    const [person, newName] = args;
    const next = setName(...args);
    expect(next.name).toEqual(newName);
    expect(person).not.toBe(next);
  });
});

types.js

export type Person = {
  name: string,
  age: number
};