}
				default:
					t.Fatalf("test %d, unknown test operation: %T", i, tf)
				}
			}

			if v.file != "" {
				want, err := os.ReadFile(v.file)
				if err != nil {
					t.Fatalf("ReadFile() = %v, want nil", err)
				}
				got := buf.Bytes()
				if !bytes.Equal(want, got) {
					t.Fatalf("incorrect result: (-got +want)\n%v", bytediff(got, want))
				}
			}
		})