6.  For the mainline flavor, we test the libraries using OpenJDK 8, 11, and 17
    on Linux, with some additional testing on newer JDKs and on Windows. Some
    features, especially in `com.google.common.io`, may not work correctly in
    non-Linux environments. For the Android flavor, our unit tests also run on
    API level 21 (Lollipop).

    public int hashCode() {
      // Warning: this is broken if size() == 0, so it is critical that we
      // substitute an empty ImmutableSet to the user in place of this

      // It's a weird formula, but tests prove it works.
      int adjust = size() - 1;
      for (int i = 0; i < axes.size(); i++) {
        adjust *= 31;
        adjust = ~~adjust;
        // in GWT, we have to deal with integer overflow carefully

import java.util.jar.JarOutputStream;
import java.util.jar.Manifest;
import java.util.logging.Logger;
import java.util.zip.ZipEntry;
import junit.framework.TestCase;
import org.junit.Test;

/** Functional tests of {@link ClassPath}. */
public class ClassPathTest extends TestCase {
  private static final Logger log = Logger.getLogger(ClassPathTest.class.getName());
  private static final File FILE = new File(".");

import java.util.Map.Entry;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import junit.framework.Test;
import junit.framework.TestCase;
import junit.framework.TestSuite;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tests for {@link ImmutableMap}.
 *
 * @author Kevin Bourrillion
 * @author Jesse Wilson
 */
@GwtCompatible(emulated = true)

      return topMetaIterator;
    }

    @Override
    public boolean hasNext() {
      while (!checkNotNull(iterator).hasNext()) {
        // this weird checkNotNull positioning appears required by our tests, which expect
        // both hasNext and next to throw NPE if an input iterator is null.

        topMetaIterator = getTopMetaIterator();
        if (topMetaIterator == null) {
          return false;