MSW + client-js Fixtures: Primary Testing Strategy

Core Principle

Drive the real transport, mock the network.

Tests in packages/playground and packages/playground-ui MUST be written as Vitest tests that exercise the real @mastra/client-js SDK, the real React Query cache, and the real component/hook code paths. The only seam we mock is the network boundary, via MSW.

This catches contract drift between the playground and @mastra/client-js at typecheck time and at test time — something vi.mock('@/hooks/...') style tests cannot do.

Priority Order

When you write or refactor a test for these packages, choose in this order: