RSpec Mocks

Verifying doubles in RSpec check that stubbed methods actually exist on the real class, whereas spies record interactions after they occur to assert calls against real objects without breaking execution flow.

To stub a method using RSpec mocks, create an instance_double for the dependency and define its return values. This isolates the unit under test by replacing real collaborators with controllable test doubles.

Use partial doubles in Ruby tests when you need to stub specific methods on a real object while keeping its original behavior intact. Standard doubles are pure stand-ins, whereas partial doubles wrap existing class instances.

Yes, using an instance_double verifies interfaces for Ruby modules and classes. It ensures stubbed methods match the real method signatures, preventing tightly coupled tests by failing if the collaborator's interface changes.

Mocking interactions with test doubles can lead to brittle tests if overused. The primary limitation is that doubles isolate units from real dependencies, meaning integration bugs between the unit and actual collaborators remain undetected.

RSpec verifying doubles fail when stubbing a missing method because they validate the method's existence against the real class. This mechanism prevents tightly coupled tests by ensuring stubbed interfaces match the actual implementation.