Test Slice with a failing reader

test/readerat.go

@@ -0,0 +1,17 @@
+// Package test contains helpers for testing parsers.
+package test
+
+import "io"
+
+type errReaderAt struct {
+	err error
+}
+
+func (r errReaderAt) ReadAt([]byte, int64) (int, error) {
+	return 0, r.err
+}
+
+// ErrReaderAt returns an [io.ReaderAt] with a ReadAt method that always returns err.
+func ErrReaderAt(err error) io.ReaderAt {
+	return errReaderAt{err: err}
+}