Do not mock what you do not own

Mocking third-party types you don't own (like framework HTTP request objects) leads to brittle, complex tests tightly coupled to implementation details. The solution is to define your own domain-specific interface wrapping the framework's generic type, then mock that owned interface instead. Using PHP and PHPUnit examples, the post demonstrates how wrapping a framework's HttpRequest in a custom SomeRequestInterface with explicit methods (getId, getAmount, getPrice) makes test doubles simpler, decouples tests from call order, and keeps production code independent of the framework's HTTP abstraction.