func (m *mockMandrillInterface) MessageSend(message gochimp.Message, async bool) ([]gochimp.SendResponse, error) {
	if message.To[0].Email == "test@domain.com" {
		return []gochimp.SendResponse{}, nil
	}
	if message.To[0].Email == "test@badhostname.com" {
		return []gochimp.SendResponse{}, fmt.Errorf(`-2: Validation error: {"message":{"from_email":"The domain portion of the email address is invalid (the portion after the @: badhostname.com)"}}`)
	}
	if message.To[0].Email == "test@badtoken.com" {
		return []gochimp.SendResponse{}, fmt.Errorf(`-1: Invalid API key`)
	}
	if message.To[0].Email == "test@badstatus.com" {
		var responses []gochimp.SendResponse
		resp := gochimp.SendResponse{
			Status: "unknown",
		}
		responses = append(responses, resp)
		return responses, nil
	}
	return []gochimp.SendResponse{}, nil
}
MessageSend is for mocking
package gomail
import (
	"fmt"
	"os"
	"testing"
	"github.com/mattbaird/gochimp"
)
type mockMandrillInterface struct{}