Adding upstream version 0.8.9.

Signed-off-by: Daniel Baumann <daniel@debian.org>

internal/testutils/failwriter.go

@@ -0,0 +1,36 @@
+package testutils
+
+import (
+	"errors"
+	"fmt"
+	"io"
+)
+
+var ErrWriteLimitReached = errors.New("reached write limit")
+
+type failWriter struct {
+	writeLimit int
+	writeCount int
+}
+
+// Close is just a dummy function to implement io.Closer.
+func (fw *failWriter) Close() error {
+	return nil
+}
+
+// Write returns an error if the write limit has been reached.
+func (fw *failWriter) Write(data []byte) (int, error) {
+	fw.writeCount++
+	if fw.writeCount > fw.writeLimit {
+		return 0, fmt.Errorf("%w: %d", ErrWriteLimitReached, fw.writeLimit)
+	}
+
+	return len(data), nil
+}
+
+// CreateFailWriter returns a io.WriteCloser that returns an error after the amount of writes indicated by writeLimit.
+func CreateFailWriter(writeLimit int) io.WriteCloser {
+	return &failWriter{
+		writeLimit: writeLimit,
+	}
+}