Sergii Makagon Ruby Developer with more than 16 years of experience. I like TDD, Clean Code, Design Patterns and Domain-Driven Design. Read more. Follow @makagon We've covered three SOLID principles so far. But this one is going to be special. Interface Segregation Principle refers to Interfaces, but we don't have it in Ruby. Should we omit this part? I don't think so, we can still learn something