*
   * <p>If the dataset contains any non-finite values ({@link Double#POSITIVE_INFINITY}, {@link
   * Double#NEGATIVE_INFINITY}, or {@link Double#NaN}) then the result is {@link Double#NaN}.
   *
   * @throws IllegalStateException if the dataset is empty
   */
  public double populationCovariance() {
    checkState(count() != 0);
    return sumOfProductsOfDeltas / count();
  }

  /**

                NullPointerException.class, () -> new UrlSource(null), "Should fail, since you must specify a url");
        assertEquals("url cannot be null", e.getMessage());
    }

    @Test
    void testGetInputStream() throws Exception {
        URL txtFile = new File("target/test-classes/source.txt").toURI().toURL();
        UrlSource source = new UrlSource(txtFile);
        try (InputStream is = source.getInputStream();

    ProxyInfo getProxy(String protocol);

    void getArtifact(Artifact artifact, ArtifactRepository repository)
            throws TransferFailedException, ResourceDoesNotExistException;

    void getArtifact(Artifact artifact, List<ArtifactRepository> remoteRepositories)
            throws TransferFailedException, ResourceDoesNotExistException;

    ArtifactRepository getMirrorRepository(ArtifactRepository repository);

    return byteSource.wasStreamOpened();
  }

  @Override
  public boolean wasStreamClosed() {
    return byteSource.wasStreamClosed();
  }

  @Override
  public Reader openStream() throws IOException {
    return new InputStreamReader(byteSource.openStream(), UTF_8);
  }

    ModelBuilderSession newSession();

    interface ModelBuilderSession {

        ModelBuilderResult build(ModelBuilderRequest request) throws ModelBuilderException;
    }

    Model buildRawModel(ModelBuilderRequest request);

     */
    @Nonnull
    Lookup getLookup();

    /**
     * Performs a clean shutdown of backing container.
     */
    @Override
    void close() throws InvokerException;

import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertNotNull;

class SerializationTest {

    @Test
    void testModelSerialization() throws Exception {
        Model model;
        try (InputStream is = getClass().getResourceAsStream("/xml/pom.xml")) {
            model = new MavenXpp3Reader().read(is);
        }

  // public so that it can be referenced in generated GWT tests.
  @Override
  public void setUp() throws Exception {
    if (setUp != null) {
      setUp.run();
    }
  }

  // public so that it can be referenced in generated GWT tests.
  @Override
  public void tearDown() throws Exception {
    if (tearDown != null) {
      tearDown.run();
    }
  }

  // public so that it can be referenced in generated GWT tests.
  @Override
  public void setUp() throws Exception {
    if (setUp != null) {
      setUp.run();
    }
  }

  // public so that it can be referenced in generated GWT tests.
  @Override
  public void tearDown() throws Exception {
    if (tearDown != null) {
      tearDown.run();
    }
  }

   *
   * @param permitsPerSecond the rate of the returned {@code RateLimiter}, measured in how many
   *     permits become available per second
   * @throws IllegalArgumentException if {@code permitsPerSecond} is negative or zero
   */
  // TODO(user): "This is equivalent to
  // {@code createWithCapacity(permitsPerSecond, 1, TimeUnit.SECONDS)}".