import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.testing.features.CollectionSize;
import java.util.Collection;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * The subject-generator interface accepted by Collection testers, for testing a Collection at one
 * particular {@link CollectionSize}.
 *
 * <p>This interface should not be implemented outside this package; {@link

-   [guava-discuss: For open-ended questions and discussion](https://groups.google.com/group/guava-discuss)

## IMPORTANT WARNINGS

1.  APIs marked with the `@Beta` annotation at the class or method level are
    subject to change. They can be modified in any way, or even removed, at any
    time. If your code is a library itself (i.e., it is used on the CLASSPATH of
    users outside your own control), you should not use beta APIs unless you

-   [guava-discuss: For open-ended questions and discussion](https://groups.google.com/group/guava-discuss)

## IMPORTANT WARNINGS

1. APIs marked with the `@Beta` annotation at the class or method level
are subject to change. They can be modified in any way, or even
removed, at any time. If your code is a library itself (i.e. it is
used on the CLASSPATH of users outside your own control), you should

    } catch (UnsupportedOperationException expected) {
    }
    expectUnchanged();
    assertTrue(collection.contains(e0()));
  }

  /*
   * AbstractCollection fails the removeAll(null) test when the subject
   * collection is empty, but we'd still like to test removeAll(null) when we
   * can. We split the test into empty and non-empty cases. This allows us to
   * suppress only the former.
   */

   * @return the contents of the container under test, for use by {@link #expectContents(Object[])
   *     expectContents(E...)} and its friends.
   */
  protected abstract Collection<E> actualContents();

  /**
   * Replaces the existing container under test with a new container created by the subject
   * generator.
   *
   * @see #resetContainer(Object) resetContainer(C)
   * @return the new container instance.
   */

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.testing.features.CollectionSize;
import java.util.Collection;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * The subject-generator interface accepted by Collection testers, for testing a Collection at one
 * particular {@link CollectionSize}.
 *
 * <p>This interface should not be implemented outside this package; {@link

    } catch (UnsupportedOperationException expected) {
    }
    expectUnchanged();
    assertTrue(collection.contains(e0()));
  }

  /*
   * AbstractCollection fails the removeAll(null) test when the subject
   * collection is empty, but we'd still like to test removeAll(null) when we
   * can. We split the test into empty and non-empty cases. This allows us to
   * suppress only the former.
   */

   * @return the contents of the container under test, for use by {@link #expectContents(Object[])
   *     expectContents(E...)} and its friends.
   */
  protected abstract Collection<E> actualContents();

  /**
   * Replaces the existing container under test with a new container created by the subject
   * generator.
   *
   * @see #resetContainer(Object) resetContainer(C)
   * @return the new container instance.
   */

/**
 * To be implemented by test generators that can produce test subjects without requiring any
 * parameters.
 *
 * @param <T> the type created by this generator.
 * @author George van den Driessche
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface TestSubjectGenerator<T extends @Nullable Object> {
  T createTestSubject();

public final class CollectorTester<
    T extends @Nullable Object, A extends @Nullable Object, R extends @Nullable Object> {
  /**
   * Creates a {@code CollectorTester} for the specified {@code Collector}. The result of the {@code
   * Collector} will be compared to the expected value using {@link Object#equals}.
   */
  public static <T extends @Nullable Object, A extends @Nullable Object, R extends @Nullable Object>