text: describe("4. About Mutability", () => {
  
    it("should expect object properties to be public and mutable", () => {
      let aPerson = { firstname: "John", lastname: "Smith" };
      aPerson.firstname = "Alan";
  
      expect(aPerson.firstname).toBe("Alan");
    });
  
    it("should understand that constructed properties are public and mutable", () => {
      function Person(firstname, lastname) {
        this.firstname = firstname;
        this.lastname = lastname;
      }
      let aPerson = new Person ("John", "Smith");
      aPerson.firstname = "Alan";
  
      expect(aPerson.firstname).toBe("Alan");
    });
  
    it("should expect prototype properties to be public and mutable", () => {
      function Person(firstname, lastname){
        this.firstname = firstname;
        this.lastname = lastname;
      }
      Person.prototype.getFullName = () => {
        return this.firstname + " " + this.lastname;
      };
  
      let aPerson = new Person ("John", "Smith");
      expect(aPerson.getFullName()).toBe(undefined);
  
      aPerson.getFullName = () => {
        return this.lastname + ", " + this.firstname;
      };
  
      expect(aPerson.getFullName()).toBe(undefined);
    });
  
    it("should know that variables inside a constructor and constructor args are private", () => {
      function Person(firstname, lastname){
        let fullName = firstname + " " + lastname;
  
        this.getFirstName = () => { return firstname; };
        this.getLastName = () => { return lastname; };
        this.getFullName = () => { return fullName; };
      }
      let aPerson = new Person ("John", "Smith");
  
      aPerson.firstname = "Penny";
      aPerson.lastname = "Andrews";
      aPerson.fullName = "Penny Andrews";
  
      expect(aPerson.getFirstName()).toBe("John");
      expect(aPerson.getLastName()).toBe("Smith");
      expect(aPerson.getFullName()).toBe("John Smith");
  
      aPerson.getFullName = () => {
        return aPerson.lastname + ", " + aPerson.firstname;
      };
  
      expect(aPerson.getFullName()).toBe("Andrews, Penny");
    });
  });
  