This repository contains a minimal reproduction of an issue where Vitest spies do not work with Prisma methods when using Vitest 4 and Prisma 6.

In Vitest 4 and Prisma 6, attempting to use vi.spyOn (or vitest.spyOn) on Prisma model methods (e.g., prisma.user.findMany) fails. This is because Prisma 6 uses Proxies for its models and methods, which vi.spyOn in Vitest 4 seems unable to resolve correctly, resulting in an error stating that it "can only spy on a function" but received undefined.

• Node.js (v20 or higher recommended)
• npm

1. Install dependencies:

   npm install

2. Generate Prisma Client:

   npx prisma generate

Run the Vitest test suite:

npm test

The test should pass, and vi.spyOn should successfully attach to the Prisma method.

The test fails with the following error:

Error: vi.spyOn() can only spy on a function. Received undefined.

Notably, this worked correctly in Vitest v3. You can verify this by downgrading Vitest and running the tests again:

npm i vitest@3
npm t