What are the Principles for Writing Testable Codes

Without any doubt, the better the code, the better the software will be. Coding is an inevitable part of software development life-cycle, which generally is the initial phase when an organization plan to develop a specific software product. The quality of codes matters a lot in the software development industry because the whole software depends upon the certain codes written by the developers. To ensure the quality of the software, special protective measures are important, in which testing is the process in limelight. 

But developers mainly have a hate relationship with testing that we believe is the main cause of highly-coupled and difficult to test code. But with the advancements in the business world, it has also made it easy for the developers to ensure the quality of the codes by the use, and implementation of the process known as code reviews. Code reviews are highly essential these days to make sure that the codes written or drafted for specific software are up to the mark and business requirements. For this purpose, code review services are a new norm. Code review services can either be incorporated into your own quality assurance efforts via making some Q/A professionals as reviewers or else you may outsource these services from a strong and trustworthy service provider. 

For enabling organizations to write testable codes, here we have come up with some of the principles that will surely help you a lot. So let’s get started;

SOLID Design Principles

The SOLID principle is one of the most famous principles in the software engineering industry, documented by Robert C. Martin (also known as Uncle Bob).

The collection of these principles can help your code to be more modular and have higher testability. Let us learn more about each of the following principles:

Single Responsibility Principle (SRP)

Each software module should have only one reason for the change.

What does that mean? Let us take an example:

Imagine that you write a program that calls an external REST API endpoint, performs some processing on the received data, and writes it to a CSV file. The naive approach might be to put everything in the same class. However, this class can be changed for several reasons:

• You may want to change the API call to another provider or change it to read from other sources (such as files).
• The processing you are performing may need to be changed.
• You may need to write the results to different outputs, perhaps in different file formats.
• In addition, you may want to have multiple types of inputs and outputs that can be interchanged based on a certain configuration or input at runtime.

For these reasons, you should decompose your application into multiple classes and interfaces. This principle can be implemented at both class and methods level. Even though you need to be cognizant in this regard and remember not to amplify it. SRP does not claim that a single module must do only one thing. It affirms to have just one reason to change. 

Open/Closed Principle (OCP)

“Your course should be expandable, but not editable”

This signifies that your design should allow for the inclusion of new and innovative features with the slightest changes to the lasting code. This can be accomplished by coding for abstract rather than concrete implementations, and by using certain design patterns (for example, decorators, visitors, and strategies). Following the “single responsibility principle” can also help you solve the problem because you isolate things.

The best way to consider this principle is to consider plug-in architecture. In this case, the development plug-in can add behavior to the system without changing any code. 

Liskov Substitution Principle (LSP)

“Objects of a superclass should be replaceable by objects of its subclasses without causing any harm to the application.”

A nice example of this principle is the problem of the square rectangle: you might want to have a Shape interface, a Rectangle that implements, and a Square that extends it, but you must ensure that the height and width are always the same. It seems good at first glimpse. Even though, this example violates the Liskov substitution principle, because even if the programming API is the same, its preconditions and postconditions are different. If you have a class or method that accepts Rectangle, you may not be able to simply pass Square to its location, because the code may assume that the height and width can be changed independently. For users of the interface, the implementation should not matter.

Interface Segregation Principle (ISP)

“Not even a single customer will be enforced to depend on methods it does not use.”

Huge interfaces must be chopped into smaller and more specific ones so that customers will only have to gather knowledge about the methods that are fascinating to them.

Following this principle helps to keep the system decoupled and it is easier to avoid violating the Liskov substitution principle.

Dependency Inversion Principle (DIP)

“High-level modules should not depend on low-level modules. Both should rely on abstraction.

Abstraction should not rely on details. The details should depend on the abstraction.”

Following this principle, you can easily replace some implementations with compatible implementations that follow the same interface. This is very useful for testing because it allows you to replace the actual implementation with test doubles. It also allows you to better respond to the changing needs.

Final Thoughts

Coming up with a software that best matches the quality requirements of the customers is the major concern for software development firms. Since to ensure the product quality some specific protective measures are important i.e to test and to test by heart and hard. Coding is the first step towards the development of software. That’s why ensuring the quality of codes is much more significant which can only be made possible via implementing the use of special code review services. Better the reviews, better the codes, that eventually sums up to the best quality software.