* work during upgrades. However it is generally inadvisable for <i>libraries</i> (which get
 * included on users' CLASSPATHs, outside the library developers' control) to do so.
 *
 * @author Kevin Bourrillion
 */
@Retention(RetentionPolicy.CLASS)
@Target({
  ElementType.ANNOTATION_TYPE,
  ElementType.CONSTRUCTOR,
  ElementType.FIELD,
  ElementType.METHOD,
  ElementType.TYPE
})
@Documented

import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Implementation of {@link ImmutableSet} with two or more elements.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
@ElementTypesAreNonnullByDefault

import org.checkerframework.checker.nullness.qual.Nullable;
import org.junit.Ignore;

/**
 * Base class for collection testers.
 *
 * @param <E> the element type of the collection to be tested.
 * @author Kevin Bourrillion
 */
@GwtCompatible
@Ignore // Affects only Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
@ElementTypesAreNonnullByDefault

 * interacting with this class directly.
 *
 * <p><b>Warning:</b> this interface can only be used to measure elapsed time, not wall time.
 *
 * @author Kevin Bourrillion
 * @since 10.0 (<a href="https://github.com/google/guava/wiki/Compatibility">mostly
 *     source-compatible</a> since 9.0)
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class Ticker {

import com.google.common.collect.testing.SampleElements.Strings;
import java.util.List;
import java.util.Set;

/**
 * Create string sets for collection tests.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class TestStringSetGenerator implements TestSetGenerator<String> {
  @Override
  public SampleElements<String> samples() {

import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * A {@code TearDownStack} contains a stack of {@link TearDown} instances.
 *
 * <p>This class is thread-safe.
 *
 * @author Kevin Bourrillion
 * @since 10.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public class TearDownStack implements TearDownAccepter {

import com.google.common.testing.TearDownAccepter;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

/**
 * Utilities for performing thread interruption in tests
 *
 * @author Kevin Bourrillion
 * @author Chris Povirk
 */
final class InterruptionUtil {
  private static final Logger logger = Logger.getLogger(InterruptionUtil.class.getName());

 * limitations under the License.
 */

package com.google.common.testing;

import com.google.common.annotations.GwtCompatible;

/**
 * An object that can perform a {@link #tearDown} operation.
 *
 * @author Kevin Bourrillion
 * @since 10.0
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface TearDown {
  /**
   * Performs a <b>single</b> tear-down operation. See test-libraries-for-java's {@code

 * interacting with this class directly.
 *
 * <p><b>Warning:</b> this interface can only be used to measure elapsed time, not wall time.
 *
 * @author Kevin Bourrillion
 * @since 10.0 (<a href="https://github.com/google/guava/wiki/Compatibility">mostly
 *     source-compatible</a> since 9.0)
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class Ticker {

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

/**
 * An object representing the differences between two maps.
 *
 * @author Kevin Bourrillion
 * @since 2.0
 */
@DoNotMock("Use Maps.difference")
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface MapDifference<K extends @Nullable Object, V extends @Nullable Object> {
  /**