t.Fatalf("wrong panic: %v", err)
			}
		default:
			t.Fatalf("unexpected panic value: %T(%v)", err, err)
		}
	}()
	b.Read(make([]byte, 100))
}

var errFake = errors.New("fake error")

type errorThenGoodReader struct {
	didErr bool
	nread  int
}

func (r *errorThenGoodReader) Read(p []byte) (int, error) {
	r.nread++
	if !r.didErr {
		r.didErr = true