send slack message in golang

slack.go

package slack

import (
	"bytes"
	"encoding/json"
	"net/http"
)

func Firehose() Slack {
	return Slack{
		url: "https://hooks.slack.com/****",
	}
}

type Payload struct {
	Text string `json:"text"`
}

type Slack struct {
	url string
}

func (s Slack) Post(payload Payload) error {
	body, err := json.Marshal(payload)
	if err != nil {
		return err
	}

	_, err = http.DefaultClient.Post(s.url, "application/json", bytes.NewReader(body))
	if err != nil {
		return err
	}
	return nil
}

slack_test.go

package slack

import (
	"encoding/json"
	"net/http"
	"net/http/httptest"
	"testing"

	"github.com/stretchr/testify/require"
)

func TestPost(t *testing.T) {
	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		payload := &Payload{}

		err := json.NewDecoder(r.Body).Decode(payload)
		require.NoError(t, err)

		require.Equal(t, "hello world:monkey_face:", payload.Text)

		w.WriteHeader(http.StatusOK)
	}))
	defer ts.Close()

	service := Slack{
		url: ts.URL,
	}

	err := service.Post(Payload{
		Text: "hello world:monkey_face:",
	})

	require.NoError(t, err)
}