import java.util.Collections;
import java.util.Iterator;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

/**
 * A utility for testing an Iterator implementation by comparing its behavior to that of a "known
 * good" reference implementation. In order to accomplish this, it's important to test a great
 * variety of sequences of the {@link Iterator#next}, {@link Iterator#hasNext} and {@link

   *
   * <p>Note: The input {@code Iterator} will be copied to an {@code ImmutableList} when this method
   * is called. This will fail if the iterator is infinite and may cause problems if the iterator
   * eagerly fetches data for each source when iterated (rather than producing sources that only
   * load data through their streams). Prefer using the {@link #concat(Iterable)} overload if
   * possible.
   *

   *
   * <p>Note: The input {@code Iterator} will be copied to an {@code ImmutableList} when this method
   * is called. This will fail if the iterator is infinite and may cause problems if the iterator
   * eagerly fetches data for each source when iterated (rather than producing sources that only
   * load data through their streams). Prefer using the {@link #concat(Iterable)} overload if
   * possible.
   *

    Iterator<String> iterator = asList("a", "b", "a").iterator();
    List<String> list = ImmutableList.copyOf(iterator);
    assertEquals(asList("a", "b", "a"), list);
  }

  public void testCopyOf_iteratorContainingNull() {
    Iterator<@Nullable String> iterator =
        Arrays.<@Nullable String>asList("a", null, "b").iterator();
    assertThrows(

    return singletonMap(key, value).entrySet().iterator().next();
  }

  private static boolean isEmpty(Iterable<?> iterable) {
    return iterable instanceof Collection
        ? ((Collection<?>) iterable).isEmpty()
        : !iterable.iterator().hasNext();
  }

  public static void assertEmpty(Iterable<?> iterable) {
    if (!isEmpty(iterable)) {
      fail("Not true that " + iterable + " is empty");
    }
  }

    expectUnchanged();
  }

  @MapFeature.Require(SUPPORTS_PUT)
  public void testPutAllOnlyCallsIteratorOnce() {
    Iterable<V> iterable =
        new Iterable<V>() {
          private boolean calledIteratorAlready = false;

          @Override
          public Iterator<V> iterator() {
            checkState(!calledIteratorAlready);
            calledIteratorAlready = true;
            return Iterators.forArray(v3());

    return singletonMap(key, value).entrySet().iterator().next();
  }

  private static boolean isEmpty(Iterable<?> iterable) {
    return iterable instanceof Collection
        ? ((Collection<?>) iterable).isEmpty()
        : !iterable.iterator().hasNext();
  }

  public static void assertEmpty(Iterable<?> iterable) {
    if (!isEmpty(iterable)) {
      fail("Not true that " + iterable + " is empty");
    }
  }

  // <Integer> needed to prevent warning :(
  private static final Iterable<Integer> iterable = Arrays.<Integer>asList();
  private static final Iterable<Integer> iterable1 = Arrays.asList(1);
  private static final Iterable<Integer> iterable12 = Arrays.asList(1, 2);
  private static final Iterable<Integer> iterable123 = Arrays.asList(1, 2, 3);
  private static final Iterable<@Nullable Integer> iterableNull = Arrays.asList((Integer) null);

  // <Integer> needed to prevent warning :(
  private static final Iterable<Integer> iterable = Arrays.<Integer>asList();
  private static final Iterable<Integer> iterable1 = Arrays.asList(1);
  private static final Iterable<Integer> iterable12 = Arrays.asList(1, 2);
  private static final Iterable<Integer> iterable123 = Arrays.asList(1, 2, 3);
  private static final Iterable<@Nullable Integer> iterableNull = Arrays.asList((Integer) null);

        lastFromForgetMeNot = null;
      }
    }

    /** Returns true if an exact reference (==) was found and removed from the supplied iterable. */
    private boolean foundAndRemovedExactReference(Iterable<E> elements, E target) {
      for (Iterator<E> it = elements.iterator(); it.hasNext(); ) {
        E element = it.next();
        if (element == target) {
          it.remove();
          return true;
        }