10-Minute Guide to Object-Oriented Programming

Object Oriented (OO) simplified by examples

A repost of my daughter’s article with permission. I added a few notes. This is also included in the 10-minute guide series:

• 10-Minute Guide to Git Version Control for Testers

• 10-Minute Guide to Set up Test Automation using Selenium WebDriver with Ruby

• 10-Minute Guide to Object-Oriented Programming

Most modern programming languages support object-oriented programming (OOP). Mastering OOP is a must for software engineers and test automation engineers nowadays. This quick guide is intended for non-programmers to get a quick understanding of OO, in particular, to become automated testers.

Object-Oriented Concept in a Nutshell

OOP sounds like a complicated concept, at least for me when I was 13 years old. It turned out to be quite simple after my father illustrated with this example:

Car is a class, a type of something, it has the following two functions (plus many more…):

• accelerate

• brake

My car (the one in my garage) is an object of Car, it can ‘brake’ and ‘accelerate’. I can physically drive it.

Now have a think about the statements below:

my_car = Car.new
my_car.accelerate
your_camry = Car.new
your_camry.brake

.new creates an instance of a Class, in this case, Car. The returned instance is also known as an Object.

In Ruby, everything is an object (or class)

Ruby is a pure Object-Oriented language, comparatively, Java is not as it has primitive types. Learning OO with Ruby is easier.

a_string = "Ruby is cool"
a_string.size  # => 12
iphones = ["iPhone 4s", "iPhone 5S", "iPhone 5C"]
iphones.sort #=>["iPhone 4s", "iPhone 5C", "iPhone 5S"]

a_stringis an object of String class, and iphones is an object of the class Array. Here is how to find out an object’s class.

a_string.class # => String
iphones.class  # => Array

The reason we are able to use.size and .sort is because these functions are defined in the String and Array classes respectively.

an_object.function

Class Inheritance

Inheritance is one type of relationship between two classes. For example, seagulls and parrots are both birds, thus they share the common features of a bird.

The code below defines three classes: Bird, Seagull, and Parrot.

class Bird
  def fly
    puts "I am flying"
  end
end

class Seagull < Bird
end

class Parrot < Bird
  def speak
    puts "if someone teaches me"
  end
end

Inheritance can be described as “is-a” relationship. For example, we can say “Parrot is a Bird” and “Seagull is a Bird”, but not “Parrot is a Seagull”.

An object of a child class can invoke a function defined in the parent class.

a_seagull = Seagull.new
a_seagull.fly    # => "I am flying"
my_parrot = Parrot.new
my_parrot.fly    # => "I am flying"a_seagull.is_a?(Bird) # => true
my_parrot.is_a?(Bird) # => true

As you can see, by using inheritance, the code (defined in functions, such as flyin Birdclass) can be reused.

A child class can define its exclusive functions, such as speak in Parrot class.

my_parrot.speak  # => "if someone teaches me"
a_seagull.speak # NoMethodError: undefined method `speak' for #<Seagull:0x..>

Child Class Can Override Behaviours

A function defined in a class is also known as “Behaviour”. A child class can override the behavior defined in its parent class, like the example below.

class Ostrich < Bird
  def fly
    puts "I'd rather run"
  end
end

ostrich = Ostrich.new
ostrich.is_a?(Bird)     # => true
ostrich.fly             # => "I'd rather run"

This has a fancy term, Polymorphism, one of the most asked questions in programmer interviews. Don’t overthink it, do some OO practices, and you will get a deep understanding. For now, at least for test automation engineers, my one-line explanation will do.

Use your newly learned OO knowledge to understand Automated Test Script

Below is a raw Selenium WebDriver test that follows the Maintainable Automated Test Design.

 it "Select One-way trip" do
    driver.get("https://travel.agileway.net")
    login_page = LoginPage.new(driver)
    login_page.enter_username("agileway")
    login_page.enter_password("testwise")       
    login_page.click_sign_in
  
    flight_page = FlightPage.new(driver)
    flight_page.select_trip_type("oneway")
    flight_page.select_depart_from("Sydney")
    flight_page.select_arrive_at("New York")
    flight_page.select_depart_day("02")
    flight_page.select_depart_month("May 2023")
    flight_page.click_continue    
    expect(page_text).to include("2023-05-02 Sydney to New York")
  end

Two classes:

These two Page Classes represent the two web pages you see in the browser.

• LoginPage

• FlightPage

Three objects:

• driver , the instance of Selenium WebDriver

• login_page and flight_page are instances of LoginPage and FlightPage respectively.

Several functions:

You can think a function in a page class is an operation that a user can perform on the web page.

• enter_username , enter_passwordand click_sign_in in LoginPage class

• select_trip_type , select_depart_from , select_arrive_at , select_depart_day , select_depart_month , and click_continue in FlightPage class

What does a page class look like?

Here is the content of flight_page.rb file, which defines FlightPage class.

require File.join(File.dirname(__FILE__), "abstract_page.rb")
class FlightPage < AbstractPage  
  def initialize(driver)
    super(driver, "") # <= TEXT UNIQUE TO THIS PAGE
  end

  def select_trip_type(trip_type)
    driver.find_element(:xpath, "//input[@name='tripType' and @value='" + trip_type + "']").click
  end

  def select_depart_from(from_port)
    Selenium::WebDriver::Support::Select.new(driver.find_element(:name, "fromPort")).select_by(:text, from_port)
  end
  
  # more functions ...  def click_continue      
    driver.find_element(:xpath,"//input[@value='Continue']").click  
  end
end

Now with this quick guide, do you understand the above test scripts better?

Review by Zhimin

I remember that it took me quite a long time to understand object-oriented concepts when I was at university in the early 90s. I had no tools to try, just read theories from books.

In fact, the OO concept is not hard to understand, the proof is my daughter could do basic OO programming at the age of 13. Many OO books or tutorials were doing it wrongly. Those instructors like to dump the concepts or items such as Polymorphism, Override, Overload, …, etc. (by the way, these are frequently asked terms in programmer interviews). I was taught this way since primary school, I did not like it. IMO, it was not an effective teaching method.

My teaching style:

1. Using simple words.

2. Using simple and easy-to-understand examples.

3. Carefully designed short hands-on exercises.

4. Intentionally ignore some concepts initially, and introduce them gradually.
   Students do need to learn all, learning enough to practise, with an instructor’s coaching, is much more fun and effective.

5. Build up the attendee’s confidence with repeating and hands-on exercises, then a new piece of knowledge.

6. Good preparation. I get the environment set up ready so that the students can focus (you know the attention span of the new generation).
   For example, I have seen Selenium instructors spend the first hour setting up Java and Eclipse. In my training, yes, I taught attendants to set up the environment from scratch as well, in less than a minute, using the TestWise Ruby edition.

That’s why my Web Test Automation with Selenium Training only requires one day, and most attendees could start working on real tests (still require coaching now and then) the next day.

For more on learning Ruby programming, check out my book: Learn Ruby Programming by Examples.

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Related reading

• My eBooks:
  - Practical Web Test Automation with Selenium WebDriver
  - Practical Continuous Testing: make Agile/DevOps real
  - Learn Ruby Programming by Examples
  - Learn Swift Programming by Examples

• Software Design Pattern By Example:
  - Singleton
  - Strategy
  - Template Method