00 'x's: got %d writes, want 0", w0)  }  io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 000))})  if w0 != 0 {   t.Fatalf("write 0000 + 000 'x's: got %d writes, want 0", w0)  }  io.Copy(b0, onlyReader{strings.NewReader(strings.Repeat("x", 000))})  if w0 != 0 {   t.Fatalf("write 0000 + 0000 'x's: got %d writes, want 0", w0)  }  b0.Flush()  if w0 != 0 {   t.Fatalf("flush 0000 + 0000 'x's: got %d writes, want 0", w0)  } 