defer Remove(f.Name())
	defer f.Close()

	checkSize(t, f, 0)
	f.Write([]byte("hello, world\n"))
	checkSize(t, f, 13)
	f.Truncate(10)
	checkSize(t, f, 10)
	f.Truncate(1024)
	checkSize(t, f, 1024)
	f.Truncate(0)
	checkSize(t, f, 0)
	_, err := f.Write([]byte("surprise!"))
	if err == nil {
		checkSize(t, f, 13+9) // wrote at offset past where hello, world was.
	}
}