Although they may seem familiar and some people tend to confuse them, Xcode UI Testing and Unit Testing differ notably.
Unit Test is the very much Unit Test we all know, since testing techniques are known. You have complete access to the Main Project and you operate its classes and frameworks like you do as a side library. You can write mocks, stubs, etc.
But UI Test is less familiar.
UI testing differs from unit testing in essential ways.
Google used to publish Apps almost instantly, no quality review whatsoever, as result, the Google Play Store was full of garbage. Crappy Apps, malicious Apps and overall useless Apps were rampant. Several scandals and privacy breaches after, Google said, no more… “We will review the Apps and ensure some quality across the board”, (turns out that, although criticized, Apple was right, all the time).
In software engineering, dependency injection is a technique in which an object receives other objects that it depends on. These other objects are called dependencies. In the typical “using” relationship the receiving object is called a client and the passed (that is, “injected“) object is called a service.
The code that passes the service to the client can be many kinds of things and is called the injector. Instead of the client specifying which service it will use, the injector tells the client what service to use. The “injection” refers to the passing of a dependency (a service) into the object (a client) that would use it.
Substitutability is a principle in object-oriented programming stating that, in a computer program, if S is a subtype of T, then objects of type T may be replaced with objects of type S (i.e. an object of type T may be substituted with any object of a subtype S) without altering any of the desirable properties of the program (correctness, task performed, etc.). More formally, the Liskov substitution principle (LSP) is a particular definition of a subtyping relation, called (strong) behavioral subtyping, that was initially introduced by Barbara Liskov in a 1987.
The Liskov Substitution Principle is the third of Robert C. Martin’s SOLID design principles. It extends the Open/Closed principle and enables you to replace objects of a parent class with objects of a subclass without breaking the application. This requires all subclasses to behave in the same way as the parent class.
“Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it.” – Robert C. Martin
A violation of this behaviour would imply your code is not SOLID and it may be prone to malfunctioning.