function UserString(obj) {

  return obj.toString();
}

The code that I want to run against:
  describe('UserString', () => {
    it('returns a string containing "name : <user's name>"', () => {
      const david= { name: 'David', age: 22, language: 'PHP' };
      const actual = createUserString(david);
      expect(actual.includes('name: David')).to.be.true;
    });
    it('returns a string containing "age : <user's age>"', () => {
      const david= { name: 'David', age: 22, language: 'PHP' };
      const actual = UserString(david);
      expect(actual.includes('age: 22')).to.be.true;
    });
    it('returns a string containing "language : <user's language>"', () => {
      const david= { name: 'David', age: 22, language: 'PHP' };
      const actual = UserString(david);
      expect(actual.includes('language: PHP')).to.be.true;
    });
    it("returns a whole string with all of the user's details", () => {
      const david= { name: 'David', age: 22, language: 'PHP' };
      let actual = UserString(david);
      expect(actual.includes('name: David, age: 22, language: Javascript')).to
        .be.true;

      const ant = { name: 'Ant', age: 28, language: 'Java' };
      actual = UserString(ant);
      expect(actual.includes('name: Ant, age: 28, language: Java')).to.be.true;
    });
  });