It seem to me that in early editions of the book whole server.go file was located in grpc folder. (instructions in the start of chapter 4 states "create directory by running mkdir -p internal/server, but this directory was already created in chapter 1 (Build commit log prototype section).

In the text of ‘test a gRPC Server and Client’ it still states: In the grpc directory create server_test.go file, while code snippet shows that file located in server directory.