What is Functional Programming?

Functional Programming (FP) is a programming paradigm that was created in the late 1950s. It’s even older than Object-Oriented Programming (OOP).

The main concepts of this paradigm are:

• Pure functions: The concrete input will produce always the same output.
• Recursion: There are no loops. In order to get this approach, the functions can call themselves using recursivity.
• Functions are First-Class: A function is treated as a variable, which means you can pass functions as function arguments.
• Variables are immutables: A variable cannot change its value once it is declared, but it’s possible to create new ones.

Imperative vs Declarative

Let’s start with the…

A mutable object can be modified after its creation, an immutable cannot.

An immutable object will remain in the same state as it was created. Design and implementation will be much easier and consistent. In the case of problems, locate a potential bug is faster due that it won’t have side-effects.

Although, creating immutable objects sometimes require more code, and it doesn’t fit in all scenarios (entities need to be mutable for example).

Mutability examples and their impacts

<?php declare(strict_types=1);final class ProductTransfer
{
    public function __construct(
        public string $name,
        public float $price,
        public array $tags,
        public \DateTime $releaseDate,
    ) {}…

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• Fork the repository into your account.

Test Doubles

A Test Double is an object that can stand-in for a real object in a test, similar to how a stunt double stands in for an actor in a movie.

As I wrote in “The importance of the Tests in our Software”, there are several types of tests. They are also known as Test Doubles instead of “Mocks”.

The five types of Test Doubles are:

TL;DR: No, and let me explain you why.

It causes bugs when refactoring due to the highly coupling

When we use reflection our tests get too fragile, we are allowing our tests to know so much information about the real implementation.
We need to hard-code the method name and we are coupling our test method to the production code.
Furthermore, we need to write a lot about boilerplate to test a simple method.

Q: I need to get at least an 80% of code coverage, how can I get it without Reflection class?
A: You should test ONLY your public methods and depend on the variables we pass, we should reach…

1.- What is a test?

A test is an empirical assertion which demonstrates the behaviour of an expected functionality from something.

The tests are classified by what they verify, the most important ones are the following:

Functional tests

• Unit test
• Component test
• Integration test
• System test
• Smoke test

Non-functional test

• Compatibility test
• Security test
• Stress test
• Usability test

A software needs all of them, but the most important concerning developers are unit, integration and functional tests.

2.- Differences between test types

Unit test