test logger

logger.go

// io.Writer implementer
type writer func(p []byte) (int, error)

func (w writer) Write(p []byte) (int, error) { return w(p) }

// magic, a testing.T writer!
func testwriter(t *testing.T) io.Writer {
	return writer(func(p []byte) (int, error) {
		t.Log(string(p))
		return 0, nil
	})
}

// magic, a testing.T logger!
func testlogger(t *testing.T) *log.Logger {
	return log.New(io.MultiWriter(testwriter(t), os.Stderr), "[test]", 0)
}

test.go

func TestSomething(t *testing.T) {
	log.SetOutput(testwriter(t))
}