In software design, understanding and addressing code smells, such as "Feature Envy", is vital for maintaining and improving code quality. Code smells are indicators of potential issues in your codebase that may hinder readability and maintainability. Feature Envy specifically arises when a method in a class has excessive interactions with the data of another class, often leading to a tangled code structure that is difficult to test and maintain.

Refactoring is the process of restructuring existing code to enhance its readability, maintainability, and performance without altering its external behavior. Common refactoring patterns, such as the Move Method, can be employed to address code smells like Feature Envy. This involves relocating methods to the class that holds the data they depend on, thus reducing unnecessary dependencies and improving cohesion.

In this course, we employ Test Driven Development (TDD) practices using Swift and XCTest. Swift's strong type system offers safety and clarity, while XCTest provides a robust framework for writing and running tests. We emphasize the TDD cycle — Red, Green, Refactor — to incrementally evolve the code with confidence, ensuring each step is supported by a comprehensive suite of tests.

Feature Envy is a code smell that occurs when a method in one class interacts too heavily with the data of another class, showing an unwarranted interest in the features of that class. This often manifests when a method accesses the properties or calls the methods of another class more frequently than it operates on its own data. This anti-pattern suggests that the method may be misplaced and that it logically belongs in the class it is so interested in.

This code smell is problematic for several reasons:

1. Poor Encapsulation: Feature Envy often breaches encapsulation, which is the foundation of object-oriented design. By reaching across class boundaries to manipulate another class's data, it undermines the principle that each class should handle its own data and behavior.