That way I could find the best ways to reduce code duplication as much as possible, to have completion everywhere, type and error checks, etc.

All in a way that provided the best development experience for all the developers.

## Requirements

import com.google.common.annotations.J2ktIncompatible;
import java.util.concurrent.Callable;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A {@link ScheduledExecutorService} that returns {@link ListenableFuture} instances from its
 * {@code ExecutorService} methods. To create an instance from an existing {@link

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import java.util.Comparator;
import java.util.SortedSet;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Utilities for dealing with sorted collections of all types.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class SortedIterables {

    FAILURE(immediateFailedFuture(new Exception()));

    final Future<Object> future;

    Result(Future<Object> result) {
      this.future = result;
    }
  }

  private enum ExceptionType {
    CHECKED(IOException.class),
    UNCHECKED(RuntimeException.class);

    final Class<? extends Exception> exceptionType;

    ExceptionType(Class<? extends Exception> exceptionType) {
      this.exceptionType = exceptionType;

import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeoutException;
import junit.framework.AssertionFailedError;
import org.checkerframework.checker.nullness.qual.Nullable;

/** Replacements for JUnit's {@code assertThrows} that work under GWT/J2CL. */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
final class ReflectionFreeAssertThrows {

import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * This class provides a skeletal implementation of the {@link Multiset} interface. A new multiset
 * implementation can be created easily by extending this class and implementing the {@link

import java.util.Collection;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Basic implementation of the {@link SetMultimap} interface. It's a wrapper around {@link
 * AbstractMapBasedMultimap} that converts the returned collections into {@code Sets}. The {@link

import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeoutException;
import junit.framework.AssertionFailedError;
import org.checkerframework.checker.nullness.qual.Nullable;

/** Replacements for JUnit's {@code assertThrows} that work under GWT/J2CL. */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
final class ReflectionFreeAssertThrows {

import java.io.Serializable;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import junit.framework.TestCase;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tests for {@code Synchronized#map}.
 *
 * @author Mike Bostock
 */
public class SynchronizedMapTest extends TestCase {

import java.util.Collection;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Basic implementation of the {@link SetMultimap} interface. It's a wrapper around {@link
 * AbstractMapBasedMultimap} that converts the returned collections into {@code Sets}. The {@link