assertSame(Ordering.natural(), copyFromSorted.valueComparator());
    assertSame(Ordering.natural(), copyFromSorted.get(1.0).comparator());
  }

  public void testComparators() {
    TreeMultimap<String, Integer> multimap = TreeMultimap.create();
    assertEquals(Ordering.natural(), multimap.keyComparator());
    assertEquals(Ordering.natural(), multimap.valueComparator());
  }

import static com.google.common.collect.Comparators.max;
import static com.google.common.collect.Comparators.min;
import static com.google.common.collect.testing.Helpers.testComparator;
import static com.google.common.truth.Truth.assertThat;
import static java.util.Arrays.asList;
import static java.util.Collections.singleton;
import static java.util.Comparator.comparing;

    // Now we don't care what order it's put the list in, only that
    // comparing any pair of elements gives the answer we expect.
    testComparator(arbitrary, list);
  }

  public void testUsingToString() {
    Ordering<Object> ordering = Ordering.usingToString();
    testComparator(ordering, 1, 12, 124, 2);
    assertEquals("Ordering.usingToString()", ordering.toString());
    assertSame(ordering, reserialize(ordering));
  }

    // Now we don't care what order it's put the list in, only that
    // comparing any pair of elements gives the answer we expect.
    testComparator(arbitrary, list);
  }

  public void testUsingToString() {
    Ordering<Object> ordering = Ordering.usingToString();
    testComparator(ordering, 1, 12, 124, 2);
    assertEquals("Ordering.usingToString()", ordering.toString());
    assertSame(ordering, reserialize(ordering));
  }

import static com.google.common.collect.testing.Helpers.assertEmpty;
import static com.google.common.collect.testing.Helpers.assertEqualInOrder;
import static com.google.common.collect.testing.Helpers.testComparator;
import static java.util.Arrays.asList;
import static java.util.Collections.emptyList;
import static java.util.Collections.singleton;

import com.google.common.annotations.GwtCompatible;
import java.util.ArrayList;

import static com.google.common.collect.testing.Helpers.assertEmpty;
import static com.google.common.collect.testing.Helpers.assertEqualInOrder;
import static com.google.common.collect.testing.Helpers.testComparator;
import static java.util.Arrays.asList;
import static java.util.Collections.emptyList;
import static java.util.Collections.singleton;

import com.google.common.annotations.GwtCompatible;
import java.util.ArrayList;

   * the given {@code comparator}.
   *
   * @see #testComparator(Comparator, List)
   */
  public static <T extends @Nullable Object> void testComparator(
      Comparator<? super T> comparator, T... valuesInExpectedOrder) {
    testComparator(comparator, asList(valuesInExpectedOrder));
  }

  /**

   * the given {@code comparator}.
   *
   * @see #testComparator(Comparator, List)
   */
  public static <T extends @Nullable Object> void testComparator(
      Comparator<? super T> comparator, T... valuesInExpectedOrder) {
    testComparator(comparator, asList(valuesInExpectedOrder));
  }

  /**

    Comparator<byte[]> comparator = UnsignedBytes.lexicographicalComparator();
    Helpers.testComparator(comparator, ordered);
    assertThat(SerializableTester.reserialize(comparator)).isSameInstanceAs(comparator);

    // The Java implementation.
    Comparator<byte[]> javaImpl = UnsignedBytes.lexicographicalComparatorJavaImpl();
    Helpers.testComparator(javaImpl, ordered);

    TreeMultimap<@Nullable String, @Nullable Integer> multimap = createPopulate();
    assertThat(multimap.values()).containsExactly(7, 3, 1, null, 0, 6, 2).inOrder();
  }

  public void testComparator() {
    TreeMultimap<@Nullable String, @Nullable Integer> multimap = createPopulate();
    assertEquals(DECREASING_INT_COMPARATOR, multimap.get("foo").comparator());