.put(IllegalStateException.class, e -> e instanceof IllegalStateException)
          .put(IndexOutOfBoundsException.class, e -> e instanceof IndexOutOfBoundsException)
          .put(NoSuchElementException.class, e -> e instanceof NoSuchElementException)
          .put(NullPointerException.class, e -> e instanceof NullPointerException)
          .put(NumberFormatException.class, e -> e instanceof NumberFormatException)

      }
    }
  }

  @CollectionSize.Require(ZERO)
  public void testEmptyMapFirst() {
    assertThrows(NoSuchElementException.class, () -> navigableMap.firstKey());
  }

  @CollectionSize.Require(ZERO)
  public void testEmptyMapLast() {
    assertThrows(NoSuchElementException.class, () -> assertNull(navigableMap.lastKey()));
  }

  @CollectionSize.Require(ONE)
  public void testSingletonMapFirst() {

          .put(IllegalStateException.class, e -> e instanceof IllegalStateException)
          .put(IndexOutOfBoundsException.class, e -> e instanceof IndexOutOfBoundsException)
          .put(NoSuchElementException.class, e -> e instanceof NoSuchElementException)
          .put(NullPointerException.class, e -> e instanceof NullPointerException)
          .put(NumberFormatException.class, e -> e instanceof NumberFormatException)

        return true;
      } catch (ClassCastException e) {
        return false;
      } catch (NoSuchElementException e) {
        return false; // concurrent change to other set
      }
    }
    return containsAll(that);
  }

  @Override
  public E first() {
    if (isEmpty()) {
      throw new NoSuchElementException();
    }
    return elements.get(0);
  }

  @Override
  public E last() {

    assertEquals(
        "next() should still return last element after peeking", "C", peekingIterator.next());

    assertThrows(NoSuchElementException.class, () -> peekingIterator.peek());
    assertThrows(NoSuchElementException.class, () -> peekingIterator.peek());
    assertThrows(NoSuchElementException.class, () -> peekingIterator.next());
  }

  public void testCantRemoveAfterPeek() {

      }
    }
  }

  @CollectionSize.Require(ZERO)
  public void testEmptySetFirst() {
    assertThrows(NoSuchElementException.class, () -> sortedSet.first());
  }

  @CollectionSize.Require(ZERO)
  public void testEmptySetLast() {
    assertThrows(NoSuchElementException.class, () -> sortedSet.last());
  }

  @CollectionSize.Require(ONE)
  public void testSingletonSetFirst() {

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.testing.features.CollectionFeature;
import com.google.common.collect.testing.features.CollectionSize;
import java.util.NoSuchElementException;
import org.junit.Ignore;

/**
 * A generic JUnit test which tests {@code remove()} operations on a queue. Can't be invoked
 * directly; please see {@link com.google.common.collect.testing.CollectionTestSuiteBuilder}.

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.DoNotMock;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * An iterator that supports a one-element lookahead while iterating.
 *
 * <p>See the Guava User Guide article on <a href=

     */
    public E getFirst() {
        if (isEmpty()) {
            throw new NoSuchElementException();
        }
        return getFirstEntry().element;
    }

    /**
     * 最後の要素を返します。
     *
     * @return 最後の要素
     */
    public E getLast() {
        if (isEmpty()) {
            throw new NoSuchElementException();
        }
        return getLastEntry().element;
    }

    /**

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.DoNotMock;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * An iterator that supports a one-element lookahead while iterating.
 *
 * <p>See the Guava User Guide article on <a href=