peachy-go/shortcircuit/shortcircuit_test.go

package shortcircuit_test

import (
	"bytes"
	"errors"
	"slices"
	"testing"

	"git.codemonkeysoftware.net/b/peachy-go/shortcircuit"
	"github.com/shoenig/test"
	"github.com/shoenig/test/must"
)

var ErrFakeFailure = errors.New("operation successfully failed")

type FailingWriter struct {
	fail       bool
	failAfter  int
	writeCalls int
}

func (f *FailingWriter) Fail() {
	f.FailAfter(0)
}

func (f *FailingWriter) FailAfter(nBytes int) {
	f.failAfter = nBytes
	f.fail = true
}

func (f *FailingWriter) Succeed() {
	f.fail = false
}

func (f *FailingWriter) Write(p []byte) (int, error) {
	f.writeCalls++
	if !f.fail {
		return len(p), nil
	}
	if f.failAfter > len(p) {
		f.failAfter -= len(p)
		return len(p), nil
	}
	n := f.failAfter
	f.failAfter = 0
	return n, ErrFakeFailure
}

func (f *FailingWriter) WriteCalls() int {
	return f.writeCalls
}

func TestWriter(t *testing.T) {
	t.Run("writes multiple times and counts total bytes written", func(t *testing.T) {
		inputs := [][]byte{
			[]byte("abcdefghi"),
			[]byte("jklmnopqr"),
			[]byte("stuvwxyz"),
		}
		var buf bytes.Buffer
		w := shortcircuit.NewWriter(&buf)
		for _, b := range inputs {
			n, err := w.Write(slices.Clone(b))
			must.NoError(t, err)
			must.False(t, w.Failed())
			must.EqOp(t, len(b), n, must.Sprint("expected Write to return length of byte slice"))
		}
		allInput := slices.Concat(inputs...)
		test.EqFunc(t, allInput, buf.Bytes(), bytes.Equal, test.Sprintf("expected written bytes to equal original bytes"))
		n, err := w.Status()
		test.EqOp(t, int64(len(allInput)), n, test.Sprint("expected total bytes written to equal total length of inputs"))
		test.NoError(t, err)
	})

	t.Run("fails without writing if error was already returned, but tries again after clearing error", func(t *testing.T) {
		w := new(FailingWriter)
		sc := shortcircuit.NewWriter(w)
		b := []byte("abcdefghi")
		expectedTotal := int64(len(b))

		// Succeed
		n, err := sc.Write(b)
		must.EqOp(t, len(b), n)
		must.NoError(t, err)
		must.EqOp(t, 1, w.WriteCalls())
		must.False(t, sc.Failed())

		// Fail
		const limit = 3
		w.FailAfter(limit)
		expectedTotal += limit

		n, err = sc.Write(b)
		must.EqOp(t, limit, n)
		must.EqOp(t, ErrFakeFailure, err)
		must.True(t, sc.Failed())
		must.EqOp(t, 2, w.WriteCalls())
		total, err := sc.Status()
		must.EqOp(t, ErrFakeFailure, err)
		must.EqOp(t, expectedTotal, total)

		// Fail again
		n, err = sc.Write(b)
		must.EqOp(t, 0, n)
		must.ErrorIs(t, err, shortcircuit.Error{})
		must.ErrorIs(t, err, ErrFakeFailure)
		must.True(t, sc.Failed())
		must.EqOp(t, 2, w.WriteCalls())
		total, err = sc.Status()
		must.EqOp(t, ErrFakeFailure, err)
		must.EqOp(t, expectedTotal, total)

		// Clear and succeed
		w.Succeed()
		sc.ClearError()
		expectedTotal += int64(len(b))

		n, err = sc.Write(b)
		must.EqOp(t, len(b), n)
		must.NoError(t, err)
		must.False(t, sc.Failed())
		must.EqOp(t, 3, w.WriteCalls())
		total, err = sc.Status()
		must.EqOp(t, expectedTotal, total)
		must.NoError(t, err)
	})
}