}

    abstract Table<Character, String, Integer> makeTable();

    @Override
    protected Map<String, Integer> makeEmptyMap() {
      return makeTable().row('a');
    }

    @Override
    protected Map<String, Integer> makePopulatedMap() {
      Table<Character, String, Integer> table = makeTable();
      table.put('a', "one", 1);
      table.put('a', "two", 2);

    }

    abstract Table<Character, String, Integer> makeTable();

    @Override
    protected Map<String, Integer> makeEmptyMap() {
      return makeTable().row('a');
    }

    @Override
    protected Map<String, Integer> makePopulatedMap() {
      Table<Character, String, Integer> table = makeTable();
      table.put('a', "one", 1);
      table.put('a', "two", 2);

// Returns nil if no checksum.
func (c ChecksumType) Hasher() hash.Hash {
	switch {
	case c.Is(ChecksumCRC32):
		return crc32.NewIEEE()
	case c.Is(ChecksumCRC32C):
		return crc32.New(crc32.MakeTable(crc32.Castagnoli))
	case c.Is(ChecksumSHA1):
		return sha1.New()
	case c.Is(ChecksumSHA256):
		return sha256.New()
	}
	return nil
}

// Trailing return whether the checksum is trailing.