Monkey Patch Mock in Golang

service.go

package service

import (
 pwi "pkg-without-interface"
)

type service struct {}

func (s *service) ListPosts() []Post {
  posts := pwi.ListPosts() // ListPosts is a pkg function.
  
  // ...

  return posts
}

type Post struct {}

service_test.go

package service

import (
  "testing"
  "bou.ke/monkey"
)

func TestListPosts(t *testing.T) {
  guard := monkey.Patch(pwi.ListPosts, func() []Post {
    fmt.Println("what the hell?") // what the *bleep*?
    
    // ...
    
    return []Post{}
  })
  defer guard.Unpatch()
  
  serivce := &service{}
  
  assert.Equal(t, []Post{}, service.ListPosts())
}

[root@control-plane monkey]# go run -N -l main.go
flag provided but not defined: -N
usage: go run [build flags] [-exec xprog] package [arguments...]
Run 'go help run' for details.

-N -1 not working, golang-1.14