Unit testing has become an essential part of software development, allowing developers to catch bugs and ensure the quality of their code. However, a common dilemma arises when it comes to writing unit tests – should the test be a friend of the tested class?
Before delving into the problem, let's first understand what a unit test and a friend class are. A unit test is a small and isolated test that verifies the functionality of a specific unit of code, usually a class or a method. On the other hand, a friend class is a class that has access to the private and protected members of another class. In simple terms, a friend class can access and modify the private variables of the class it is friends with.
Now, the question arises, why would someone want to make a unit test a friend of the tested class? The answer is simple – to gain access to private variables and methods, making it easier to test them. By doing so, developers can avoid the hassle of creating getters and setters for private variables or changing the access modifiers of methods to public, which goes against the principle of encapsulation.
While making a unit test a friend class may seem like a convenient solution, it brings with it a host of problems. One of the main problems is the violation of the single responsibility principle. This principle states that a class should have only one reason to change. By making a unit test a friend class, it becomes tightly coupled with the tested class, and any changes made to the tested class can potentially break the unit test. This results in the unit test needing to be updated every time the tested class is modified, increasing the code maintenance effort.
Moreover, making a unit test a friend class also goes against the concept of test independence. Unit tests should be independent of each other, meaning they should not rely on the internal state of other tests. By making a unit test a friend of the tested class, it can access and modify the private variables of the tested class, which can lead to unexpected behavior in other unit tests.
Another issue with making a unit test a friend class is the potential security risks it poses. When a friend class can access and modify private variables, it can also be used by malicious actors to manipulate the code and cause harm to the system.
Furthermore, making a unit test a friend class can also hinder the refactoring process. Refactoring is the process of improving the code without changing its functionality. By making a unit test a friend of the tested class, any changes made to the code may require the unit test to be updated, making the refactoring process more cumbersome.
In conclusion, while making a unit test a friend of the tested class may seem like a convenient way to access private variables and methods, it brings with it various problems. Violation of the single responsibility principle, test independence, security risks, and hindering the refactoring process are some of the issues that arise when unit tests are made friends of the tested class. Therefore, it is best to avoid making unit tests friends of the tested class and instead opt for other methods of testing private variables and methods, such as using reflection. By doing so, developers can ensure clean, maintainable, and secure code while still achieving effective unit testing.
