person.spec.ts

import Person from "./person";

describe('a person', () => {
  it('should create default', () => {
    let person = new Person();
    let defaultPerson = new Person({name: "default", address: "default", age: 0});
    expect(person).toEqual(defaultPerson);
  });

  it('should create with parameters', () => {
    let person = new Person({name: "foo", address: "bar", age: 20});
    let defaultPerson = new Person({name: "foo", address: "bar", age: 20});
    expect(person).toEqual(defaultPerson);
  });
});

person.ts

export default class Person {
  public name: string = "default"
  public address: string = "default"
  public age: number = 0;

  public constructor(init:Partial<Person> = {} as Partial<Person>) {
    this.name = init.name || this.name;
    this.address = init.address || this.address;
    this.age = init.age || this.age;
  }
}