}

  public void testEntryEquals() {
    Cell<String, Integer, Character> entry = immutableCell("foo", 1, 'a');

    new EqualsTester()
        .addEqualityGroup(entry, immutableCell("foo", 1, 'a'))
        .addEqualityGroup(immutableCell("bar", 1, 'a'))
        .addEqualityGroup(immutableCell("foo", 2, 'a'))
        .addEqualityGroup(immutableCell("foo", 1, 'b'))
        .addEqualityGroup(

                    return new SampleElements<>(
                        immutableCell("bar", 1, 'a'),
                        immutableCell("bar", 2, 'b'),
                        immutableCell("bar", 3, (Character) null),
                        immutableCell("bar", 4, 'b'),
                        immutableCell("bar", 5, 'b'));
                  }

                  @Override

      if (cell instanceof Tables.ImmutableCell) {
        checkNotNull(cell.getRowKey(), "row");
        checkNotNull(cell.getColumnKey(), "column");
        checkNotNull(cell.getValue(), "value");
        @SuppressWarnings("unchecked") // all supported methods are covariant
        Cell<R, C, V> immutableCell = (Cell<R, C, V>) cell;
        cells.add(immutableCell);
      } else {

      Cell<R, C, V> immutableCell(
          @ParametricNullness R rowKey,
          @ParametricNullness C columnKey,
          @ParametricNullness V value) {
    return new ImmutableCell<>(rowKey, columnKey, value);
  }

  static final class ImmutableCell<
          R extends @Nullable Object, C extends @Nullable Object, V extends @Nullable Object>