test/support/builders: Effectively build warnings as an Error
test/support/builders: Effectively build warnings as an Error

Return both:
- the error for stubbing
- the warnings for assertions

nono/cozy-desktop,cozy-labs/cozy-desktop,cozy-labs/cozy-desktop,nono/cozy-desktop,nono/cozy-desktop,cozy-labs/cozy-desktop,nono/cozy-desktop,cozy-labs/cozy-desktop