private static final class AlwaysEqual extends Ordering<@Nullable Object>
      implements Serializable {
    private static final AlwaysEqual INSTANCE = new AlwaysEqual();

    @Override
    @SuppressWarnings("UnusedVariable") // intentionally weird Comparator
    public int compare(@Nullable Object o1, @Nullable Object o2) {
      return 0;
    }

    @Override

import com.google.common.collect.testing.WrongType;
import com.google.common.collect.testing.features.CollectionFeature;
import com.google.common.collect.testing.features.CollectionSize;
import org.jspecify.annotations.Nullable;
import org.junit.Ignore;

/**
 * Common parent class for {@link ListIndexOfTester} and {@link ListLastIndexOfTester}.
 *
 * @author Chris Povirk
 */
@GwtCompatible

        // Default constructor
    }

    /**
     * Creates an OptionalEntity from a nullable entity.
     *
     * @param <T> the type of the entity
     * @param entity the entity (can be null)
     * @return the OptionalEntity
     */
    public static <T> OptionalEntity<T> ofNullable(final T entity) {
        return OptionalEntity.ofNullable(entity, () -> {});
    }

import com.google.errorprone.annotations.OverridingMethodsMustInvokeSuper;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;
import org.junit.Ignore;

/**
 * Base class for testers of classes (including {@link Collection} and {@link java.util.Map Map})
 * that contain elements.
 *
 * @param <C> the type of the container

import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

/** Replacements for JUnit's {@code assertThrows} that work under GWT/J2CL. */
@GwtCompatible
@NullMarked
final class ReflectionFreeAssertThrows {
  interface ThrowingRunnable {
    void run() throws Throwable;
  }

  interface ThrowingSupplier {
    @Nullable Object get() throws Throwable;
  }

  @CanIgnoreReturnValue

package com.google.common.collect.testing;

import com.google.common.annotations.GwtCompatible;
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

import java.util.List;
import java.util.Set;
import java.util.logging.Logger;
import junit.framework.Test;
import junit.framework.TestCase;
import junit.framework.TestSuite;
import org.jspecify.annotations.Nullable;

/**
 * Creates, based on your criteria, a JUnit test suite that exhaustively tests the object generated
 * by a G, selecting appropriate tests by matching them against specified features.
 *

  public void testPutAllNullForbidden() {
    assertThrows(NullPointerException.class, () -> multimap().putAll(null, singletonList(v3())));
  }

  @SuppressWarnings("EmptyList") // ImmutableList doesn't support nullable element types
  @MapFeature.Require(SUPPORTS_PUT)
  public void testPutAllEmptyCollectionOnAbsentKey() {
    assertFalse(multimap().putAll(k3(), Collections.<V>emptyList()));
    expectUnchanged();
  }

import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.stream.Collector;
import jsinterop.annotations.JsMethod;
import org.jspecify.annotations.Nullable;

/**
 * GWT emulated version of {@link com.google.common.collect.ImmutableSet}. For the unsorted sets,
 * they are thin wrapper around {@link java.util.Collections#emptySet()}, {@link

  }

  static <K extends @Nullable Object, V extends @Nullable Object>
      Map<K, V> newLinkedHashMapWithExpectedSize(int expectedSize) {
    return Maps.newLinkedHashMapWithExpectedSize(expectedSize);
  }

  static <E extends @Nullable Object> Set<E> newHashSetWithExpectedSize(int expectedSize) {
    return Sets.newHashSetWithExpectedSize(expectedSize);
  }

  static <E extends @Nullable Object> Set<E> newConcurrentHashSet() {