Spies don't work on prisma client methods in vitest 4 #9439
Description
Describe the bug
When trying to spy on Prisma client methods, vitest throws the following error:
const prisma = new PrismaClient();
const spy = vitest.spyOn(prisma.user, 'findMany')Error: vi.spyOn() can only spy on a function. Received undefined.This setup works as expected in vitest v3, but no longer seems to behave work in vitest v4 versions.
This can be verified by installing vitest@3 in the reproduction repository and running the tests again.
Reproduction
https://github.com/schoero/repro-vitest-prisma-spies
System Info
System:
OS: macOS 15.7.3
CPU: (8) arm64 Apple M2
Memory: 107.09 MB / 24.00 GB
Shell: 5.9 - /bin/zsh
Binaries:
Node: 24.5.0 - /Users/schoero/.volta/tools/image/node/24.5.0/bin/node
Yarn: 1.22.22 - /Users/schoero/.volta/tools/image/yarn/1.22.22/bin/yarn
npm: 11.5.1 - /Users/schoero/.volta/tools/image/node/24.5.0/bin/npm
pnpm: 10.16.0 - /Users/schoero/.volta/bin/pnpm
bun: 1.3.5 - /opt/homebrew/bin/bun
Browsers:
Chrome: 143.0.7499.194
Firefox: 142.0
Safari: 26.2
npmPackages:
vitest: ^4.0.17 => 4.0.17Used Package Manager
npm
Validations
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- The provided reproduction is a minimal reproducible example of the bug.