*     class under test.
   */
  protected abstract Map<K, V> makePopulatedMap() throws UnsupportedOperationException;

  /**
   * Creates a new key that is not expected to be found in {@link #makePopulatedMap()}.
   *
   * @return a key.
   * @throws UnsupportedOperationException if it's not possible to make a key that will not be found
   *     in the map.

   *     class under test.
   */
  protected abstract Map<K, V> makePopulatedMap() throws UnsupportedOperationException;

  /**
   * Creates a new key that is not expected to be found in {@link #makePopulatedMap()}.
   *
   * @return a key.
   * @throws UnsupportedOperationException if it's not possible to make a key that will not be found
   *     in the map.

  protected abstract SortedMap<K, V> makeEmptyMap() throws UnsupportedOperationException;

  @Override
  protected abstract SortedMap<K, V> makePopulatedMap() throws UnsupportedOperationException;

  @Override
  protected SortedMap<K, V> makeEitherMap() {
    try {
      return makePopulatedMap();
    } catch (UnsupportedOperationException e) {
      return makeEmptyMap();
    }
  }

  public void testTailMapWriteThrough() {

    RowSortedTable<String, Integer, Character> original = TreeBasedTable.create();
    return unmodifiableRowSortedTable(original);
  }

  @Override
  protected SortedMap<String, Map<Integer, Character>> makePopulatedMap() {
    RowSortedTable<String, Integer, Character> table = TreeBasedTable.create();
    table.put("foo", 1, 'a');
    table.put("bar", 1, 'b');
    table.put("foo", 3, 'c');

    Table<String, Integer, Character> original = HashBasedTable.create();
    return unmodifiableTable(original);
  }

  @Override
  protected Map<String, Map<Integer, Character>> makePopulatedMap() {
    Table<String, Integer, Character> table = HashBasedTable.create();
    table.put("foo", 1, 'a');
    table.put("bar", 1, 'b');
    table.put("foo", 3, 'c');
    return unmodifiableTable(table).rowMap();
  }

    @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);
      table.put('a', "three", 3);
      table.put('b', "four", 4);

    @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);
      table.put('a', "three", 3);
      table.put('b', "four", 4);

    Table<Character, String, Integer> table = HashBasedTable.create();
    return transformValues(table, TableCollectionTest.DIVIDE_BY_2);
  }

  @Override
  protected Map<String, Integer> makePopulatedMap() {
    Table<Character, String, Integer> table = HashBasedTable.create();
    table.put('a', "one", 2);
    table.put('a', "two", 4);
    table.put('a', "three", 6);
    table.put('b', "four", 8);

    RowSortedTable<Integer, String, Character> original = TreeBasedTable.create();
    return unmodifiableRowSortedTable(original);
  }

  @Override
  protected Map<String, Map<Integer, Character>> makePopulatedMap() {
    RowSortedTable<Integer, String, Character> table = TreeBasedTable.create();
    table.put(1, "foo", 'a');
    table.put(1, "bar", 'b');
    table.put(3, "foo", 'c');

    Table<String, Integer, Character> original = HashBasedTable.create();
    return unmodifiableTable(original);
  }

  @Override
  protected Map<String, Map<Integer, Character>> makePopulatedMap() {
    Table<String, Integer, Character> table = HashBasedTable.create();
    table.put("foo", 1, 'a');
    table.put("bar", 1, 'b');
    table.put("foo", 3, 'c');
    return unmodifiableTable(table).rowMap();
  }