mock-slack-post-message.go

package service

import (
	"github.com/slack-go/slack"
)

func (s *SlackService) PostMessage(channel string, attachment slack.Attachment) (string, string, error) {
	// ... your implementation here
	return s.api.PostMessage(
		channel,
		slack.MsgOptionAttachments(attachment),
		slack.MsgOptionAsUser(true),
	)
}

mock-slack-service.go

package service

import "github.com/slack-go/slack"

type SlackAPI interface {
	PostMessage(channelID string, options ...slack.MsgOption) (string, string, error)
}

type SlackService struct {
	api SlackAPI
}

func NewSlackService(api SlackAPI) *SlackService {
	return &SlackService{
		api: api,
	}
}