}
		if header.Typeflag != TypeReg {
			t.Fatalf("Typeflag should've been %d, found %d", TypeReg, header.Typeflag)
		}
	}
}

// failOnceWriter fails exactly once and then always reports success.
type failOnceWriter bool

func (w *failOnceWriter) Write(b []byte) (int, error) {
	if !*w {
		return 0, io.ErrShortWrite
	}
	*w = true
	return len(b), nil
}

		if err := w.SetComment(test.comment); err != nil {
			if test.ok {
				t.Fatalf("SetComment: unexpected error %v", err)
			}
			continue
		} else {
			if !test.ok {
				t.Fatalf("SetComment: unexpected success, want error")
			}
		}

		if err := w.Close(); test.ok == (err != nil) {
			t.Fatal(err)
		}

		if w.closed != test.ok {
			t.Fatalf("Writer.closed: got %v, want %v", w.closed, test.ok)
		}