* undocumented and subject to change.
   */
  public static <R, C, V> ImmutableTable<R, C, V> copyOf(
      Table<? extends R, ? extends C, ? extends V> table) {
    if (table instanceof ImmutableTable) {
      @SuppressWarnings("unchecked")
      ImmutableTable<R, C, V> parameterizedTable = (ImmutableTable<R, C, V>) table;
      return parameterizedTable;
    } else {
      return copyOf(table.cellSet());

import com.google.common.annotations.GwtCompatible;
import junit.framework.TestCase;

/**
 * Tests {@link ImmutableTable}
 *
 * @author Gregory Kick
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class AbstractImmutableTableTest extends TestCase {

  abstract Iterable<ImmutableTable<Character, Integer, String>> getTestInstances();

  public final void testClear() {

  public void testBuilder_withImmutableCell() {
    ImmutableTable.Builder<Character, Integer, String> builder = new ImmutableTable.Builder<>();
    assertEquals(
        ImmutableTable.of('a', 1, "foo"), builder.put(immutableCell('a', 1, "foo")).build());
  }

  public void testBuilder_withImmutableCellAndNullContents() {
    ImmutableTable.Builder<Character, Integer, String> builder = new ImmutableTable.Builder<>();
    assertThrows(

      new DenseImmutableTable<>(CELLS.asList(), ROW_SPACE, COLUMN_SPACE);

  @Override
  Iterable<ImmutableTable<Character, Integer, String>> getTestInstances() {
    return ImmutableList.<ImmutableTable<Character, Integer, String>>of(SPARSE, DENSE);
  }

  public void testCellSet() {
    for (ImmutableTable<Character, Integer, String> testInstance : getTestInstances()) {
      assertEquals(CELLS, testInstance.cellSet());
    }

 */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
public class EmptyImmutableTableTest extends AbstractImmutableTableTest {
  private static final ImmutableTable<Character, Integer, String> INSTANCE = ImmutableTable.of();

  @Override
  Iterable<ImmutableTable<Character, Integer, String>> getTestInstances() {
    return ImmutableSet.of(INSTANCE);
  }

  public void testHashCode() {
    assertEquals(0, INSTANCE.hashCode());

  }

  public void testEqualsObject() {
    new EqualsTester()
        .addEqualityGroup(testTable, HashBasedTable.create(testTable))
        .addEqualityGroup(ImmutableTable.of(), HashBasedTable.create())
        .addEqualityGroup(HashBasedTable.create(ImmutableTable.of('A', 2, "")))
        .testEquals();
  }

  @GwtIncompatible // ArrayTable
  public void testEqualsObjectNullValues() {
    new EqualsTester()

          .put(BiMap.class, ImmutableBiMap.of())
          .put(ImmutableBiMap.class, ImmutableBiMap.of())
          .put(Table.class, ImmutableTable.of())
          .put(ImmutableTable.class, ImmutableTable.of())
          .put(RowSortedTable.class, Tables.unmodifiableRowSortedTable(TreeBasedTable.create()))
          .put(ClassToInstanceMap.class, ImmutableClassToInstanceMap.builder().build())

    }
  }

  private static final class MockEquivalence extends Equivalence<Object> {
    final ImmutableTable.Builder<Object, Object, Boolean> equivalentExpectationsBuilder =
        ImmutableTable.builder();
    final ImmutableMap.Builder<Object, Integer> hashExpectationsBuilder = ImmutableMap.builder();
    ImmutableTable<Object, Object, Boolean> equivalentExpectations;
    ImmutableMap<Object, Integer> hashExpectations;

    }
  }

  private static final class MockEquivalence extends Equivalence<Object> {
    final ImmutableTable.Builder<Object, Object, Boolean> equivalentExpectationsBuilder =
        ImmutableTable.builder();
    final ImmutableMap.Builder<Object, Integer> hashExpectationsBuilder = ImmutableMap.builder();
    ImmutableTable<Object, Object, Boolean> equivalentExpectations;
    ImmutableMap<Object, Integer> hashExpectations;

import com.google.common.annotations.J2ktIncompatible;
import java.util.Map;

/**
 * An implementation of {@link ImmutableTable} that holds a single cell.
 *
 * @author Gregory Kick
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
class SingletonImmutableTable<R, C, V> extends ImmutableTable<R, C, V> {
  final R singleRowKey;
  final C singleColumnKey;
  final V singleValue;