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How To Write a Testable Code and Why it Matters

Hello, fellas! How is the world? How are things going? I hope everything is well. Today we are going to discuss the topic “How to Write Testable Code and Why It Matters. I will clarify the most important issues. Every domain has its personal best methods and systems. Once, Elan Kay, American computer scientist said:

Technology is anything that wasn’t around when you were born.

In my opinion, programming is the art of translating business elements into a computer language. Nevertheless, in this topic, I would like to concentrate on programming from different aspects. And I think it requires more attention.

So, don’t waste your time, let’s get started.

What is Unit testing?

Have you ever heard about unit testing? I believe there are still some people who are not well informed about it. So, what is Unit Testing? I know that many developers have a hate relationship with testing. But, I think the main reason for that is the code that is highly-coupled and hard to test.

A unit test is a program that instantiates a small part of our application and verifies its function individually from other parts. You must remember this module is performed only by different developers. A typical unit test includes 3 phases: firstly, it initializes a small part of an application that is necessary to be tested, then it uses some stimulus to the system under test, and lastly, it keeps the resulting behavior.

But let’s discuss what is unit in detail. A unit is the smallest testable part of any software. It regularly has one or a few facts and usually an individual output. Testing is an investment, and you want our properties to be important in the future.

Now let’s go on to the next position. I understand you’re anxious to get as much information as possible.

How to Write a Testable Code

First of all, when you hear testable code, what I mean is code that can be tested programmatically and in a very granular way.

Writing unit tests is pretty simple if the code is testable and well-structured. And now be ready for I want to introduce a few points on how to write testable code. A few principles to keep in mind when writing this code:

1. Write functional pieces without side effects

You must think of each code block as a useful piece that shouldn’t cause any side results. If you have any side effects should be separated and protected.

2. Use Inversion of Control

The big advantage of using Inversion of Control or Dependency Injection via constructor parameter. You easily can mock all those dependencies in your unit tests.

3. Adhere to the SOLID principles

The SOLID-principles are guidelines for writing a good Object-Oriented code. The most essential principle for writing testable code is the single responsibility principle. You should split your code into small task-oriented blocks.

4. Write the unit tests first

One of the core principles of Test-Driven Development is that you should write your unit tests before you write the original code. This will force you to write testable code.

5. Try not to use static methods or variables

Static methods can be difficult to mock out. Avoid them if possible. Static variables leave a global state and should only be used in very specific cases.

What are some advantages of testable code?

Well, for one thing, it suggests that you can automate the verification process so you can keep our software in an always ready to release state. It also makes last-minute changes, the kind of changes that are usually very important on a project, small and cost-free. These are the same kind of changes that are usually exorbitantly expensive to make late in a development project that doesn’t use automated regression testing. Writing testable code means that the smallest components are independently verifiable. To do this, each element must have its dependencies injected into it.

You can see Testable code it’s well encapsulated and in charge of its state. In addition, it’s especially defined in its place so that it’s honest to support and extend.


Summing up, I’d like to say that I hope this post gave you some grounds about writing testable code and that by understanding these principles and guidelines you will be able to have a more clean, maintainable, and testable codebase.  I tried to highlight the most important facts, which can be useful for you.  Let’s remember a few principles how to write a testable code:

  1. Write functional pieces without side effects
  2. Use Inversion of Control
  3. Adhere to the SOLID principles
  4. Write the unit tests first
  5. Try not to use static methods or variables

I reckon it is also necessary to notice that the unit testing reduces the costs of testing, makes the process of development faster as well as the better design.

Thank you for reading! Stay healthy!

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