diffpanicwriter.go

package diffpanicwriter

import (
  "testing"
  "io"
  "errors"
)

type DiffPanicWriter struct {
	pos    int
	golden []byte
	out    io.Writer
	t      *testing.T
}

func (w *DiffPanicWriter) Write(b []byte) (int, error) {
	w.t.Helper()
	sz := len(b)
	if len(w.golden) < sz {
		sz = len(w.golden)
	}
	for i := 0; i < len(b); i++ {
		if w.golden[w.pos] != b[i] {
			panic(fmt.Sprintf("tested data different than golden data: pos=%d: \n%x != %x", w.pos, w.golden[w.pos], b[i]))
		}
		w.pos++
		if len(b) < i-1 {
			return 0, errors.New("can't write 1 byte into writer")

		}
		n, err := w.out.Write([]byte{b[i]})
		if n != 1 && err != nil {
			return n, err
		}
	}

	return len(b), nil
}