With XUI_DB_TYPE=postgres every test package shared one database and worked in public. Go runs package test binaries concurrently, so migrations raced and rows a previous run left behind leaked into the next.
testpg.IsolatePackage creates a schema for the calling package, puts it first on search_path and drops it when the package finishes. It returns at once unless XUI_DB_TYPE is postgres. internal/web/service's TestMain adopts it.
n0ctal