how-to-test-slog

gistfile1.txt

package rds

import (
	log "log/slog"
)

func Process(input string) string {
	log.Info("process")
	return input
}

---
package rds_test

import (
	"bytes"
	"fmt"
	"log/slog"
	"testing"

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

func TestProcessLogging(t *testing.T) {
	var buf bytes.Buffer
	th := slog.NewTextHandler(&buf, nil)
	slog.SetDefault(slog.New(th))
	_ = Process("hello")
	assert.Contains(t, buf.String(), "level=INFO msg=process")
}

func TestProcessLoggingMocking(t *testing.T) {
	wr := WriterC{}
	th := slog.NewTextHandler(&wr, nil)
	slog.SetDefault(slog.New(th))
	_ = Process("hello")
	assert.Equal(t, wr.CountInfo, 1)
}

type WriterC struct {
	CountInfo int
}

// Write overrides behaviour of Writer interface
func (w *WriterC) Write(p []byte) (n int, err error) {
	if strings.Contains(strings.ToLower(string(p)), "info") {
		w.CountInfo += 1
	}
	return len(p), nil
}