I got the same error message for "please make sure that outDir in your tsconfig is neither '' or '.'. You can also configure Jest config option transformIgnorePatterns to inform ts-jest to transform"

Hope to share how I solved this for Fastify and Typescript users.

• Pre-required : tsconfig and jest config looks fine.
• Why this happen? I am using package "json-schema-to-ts", and when I import a type into a service, I import from the specific schema path, instead of index.ts(your json-schema-to-ts entry point). The import service code line in jest got confused on where the tsconfig is.
• How to solve? Be aware of the types you imported in your service. export from index.ts and import from index.ts.