test-doubles-design

What problem does it solve?

This Skill helps you design test doubles (dummy, stub, spy, mock, fake) so your tests verify the right kind of truth without becoming fragile, misleading, or overly coupled to implementation details.

Core Features & Use Cases

• Select the correct double type based on whether you need state verification or interaction verification, including the practical tradeoffs that drive the choice.
• Avoid common testing failures like over-mocking, false confidence from rigid mocks, and divergence from real collaborator behavior.
• Prefer fakes when possible by using working in-memory stand-ins as the robust middle ground between fully mocked interactions and heavyweight real collaborators.
• Use the right boundary with related disciplines, clarifying what this Skill covers (double design) versus what it deliberately does not (test levels, what to test, or TDD practice mechanics).

Quick Start

Ask the skill to recommend which test double fits your scenario and to explain whether your test should verify state or interaction using the five-kind taxonomy.