Dual Testing

Language-agnostic strategy for testing code at the boundary with external infrastructure (databases, APIs, queues): integration tests with real infrastructure (e.g. Testcontainers) prove the full chain works for happy paths; unit/slice tests with mocks prove error-handling and mapping logic (domain error to status, input validation, infra failure). Works in any language/framework — Go, .NET/C#, Java, Python, TypeScript and more — with concrete references for Go, .NET (ASP.NET Core) and Java (Spring Boot) and an explicit path to adapt when no reference matches your language. Apply when designing a test strategy, creating a handler/feature/worker that needs tests, or deciding what type of test a scenario needs. Triggers: 'dual testing', 'integration vs unit', 'testcontainers vs mocks', 'what type of test', 'where should this test go', 'error path coverage'. Does NOT trigger on writing individual test assertions or test naming conventions (use test-namer for those).

mkdir -p ~/.claude/skills/dual-testing
curl -L https://claudskills.com/skills/dual-testing/SKILL.md \
  -o ~/.claude/skills/dual-testing/SKILL.md

@misc{dual-testing-2026,
  author    = {mryll},
  title     = {Dual Testing [Claude Code skill]},
  year      = {2026},
  publisher = {ClaudSkills},
  url       = {https://claudskills.com/skills/dual-testing/}
}