if err != nil {
					if !test.wantErr {
						t.Errorf("%s: %v", path, err)
					}
					sawErr = true
					return nil
				}
				files = append(files, path)
				return nil
			})
			if err != nil {
				t.Errorf("fs.WalkDir error: %v", err)
			}
			if test.wantErr && !sawErr {
				t.Error("succeeded but want error")

						err = nil // Expected error
					}
					break
				}
				hdrs = append(hdrs, hdr)

				if v.chksums == nil {
					continue
				}
				h := md5.New()
				_, err = io.CopyBuffer(h, tr, rdbuf) // Effectively an incremental read
				if err != nil {
					break
				}
				chksums = append(chksums, fmt.Sprintf("%x", h.Sum(nil)))
			}

			for i, hdr := range hdrs {

			// should not happen
			t.Fatal(err)
		}
		tt.f(reader)
		err := reader.UnreadRune()
		if err == nil {
			t.Errorf("Unreading after %s: expected error", tt.name)
		}
	}
}

func TestReaderDoubleUnreadRune(t *testing.T) {
	buf := NewBuffer([]byte("groucho"))
	if _, _, err := buf.ReadRune(); err != nil {
		// should not happen
		t.Fatal(err)
	}