test-third-partylisted

# Third-Party Libraries Base principles: [test-isolation-base](../test-isolation-base/SKILL.md) **Never substitute a pure third-party library.** Substituting it pins your _belief_ about the library, which survives every upgrade that breaks the belief. If the library reaches the network, the clock, or the disk, inject that boundary instead of faking the whole library. Example: instead of mocking `axios`, inject an `HttpClient` abstraction and stub that. The abstraction is thin (one method), the stub is trivial, and the test pins the contract you own rather than the library's internals. Per-language: [TypeScript](references/typescript.md)