* @throws IllegalArgumentException if the stream consists of two or more elements.
   * @throws NullPointerException if any element in the stream is {@code null}.
   * @return {@code Optional.of(onlyElement)} if the stream has exactly one element (must not be
   *     {@code null}) and returns {@code Optional.empty()} if it has none.
   */
  @SuppressWarnings("unchecked")
  public static <T> Collector<T, ?, Optional<T>> toOptional() {

    checkNotNull(throwable);
    if (declaredType.isInstance(throwable)) {
      throw declaredType.cast(throwable);
    }
  }

  /**
   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@code
   * declaredType}. Example usage:
   *
   * <pre>
   * try {
   *   someMethodThatCouldThrowAnything();
   * } catch (IKnowWhatToDoWithThisException e) {

	}

	// Assert new checksum matches the content
	matchError := chksmOut.Matches(myData, 0)
	if matchError != nil {
		t.Fatalf("Checksum mismatch on chksmOut: %v", matchError)
	}

	// Assert they are exactly equal
	if !chksmOut.Equal(chksm) {
		t.Fatalf("Checksum mismatch: expected %+v, got %+v", chksm, chksmOut)
	}
}

// TestChecksumSerializeDeserializeMultiPart checks AppendTo can be reversed by ChecksumFromBytes

 *    prefix at all (`publicobject.com`). For most applications this is the best way to configure
 *    certificate pinning.
 *
 *  * **Exactly one subdomain**: Use a single asterisk like `*.publicobject.com` to match exactly
 *    one prefix (`www.publicobject.com`, `api.publicobject.com`). Be careful with this approach as

     */
    void setCacheMap(Map<String, DfsReferralDataInternal> map);

    /**
     * Replaces the entry with key in the cache map with this referral
     */
    void replaceCache();

    /**
     * Not exactly sure what that is all about, certainly legacy stuff
     *
     * @return resolveHashes
     */
    boolean isResolveHashes();

    /**
     * Check if this referral needs to be resolved further
     *

//   - Exactly 0 bytes are read and EOF is hit.
//   - Exactly 1 block of zeros is read and EOF is hit.
//   - At least 2 blocks of zeros are read.
func (tr *Reader) readHeader() (*Header, *block, error) {
	// Two blocks of zero bytes marks the end of the archive.
	if _, err := io.ReadFull(tr.r, tr.blk[:]); err != nil {
		return nil, nil, err // EOF is okay here; exactly 0 bytes read
	}

import com.google.common.annotations.J2ktIncompatible;
import com.google.common.base.Preconditions;
import org.jspecify.annotations.Nullable;

/**
 * Implementation of {@link ImmutableSet} with exactly one element.
 *
 * @author Kevin Bourrillion
 * @author Nick Kralevich
 */
@GwtCompatible
@SuppressWarnings("serial") // uses writeReplace(), not default serialization

        final List<String> indices = (List<String>) method.invoke(suggester, aliasName);

        assertNotNull("Indices list should not be null", indices);
        assertEquals("Should find exactly one index", 1, indices.size());
        assertEquals("Should return correct index name", indexName, indices.get(0));

        // Cleanup
        client.admin().indices().prepareDelete(indexName).execute().actionGet();

   */
  protected final void expectContents(E... elements) {
    expectContents(asList(elements));
  }

  /**
   * Asserts that the collection under test contains exactly the given elements, respecting
   * cardinality but not order. Subclasses may override this method to provide stronger assertions,
   * e.g., to check ordering in lists, but realize that <strong>unless a test extends {@link

        byte[] buf = newBuffer(10);

        int written = cmd.writeParametersWireFormat(buf, 0);
        assertEquals(2, written, "writeParametersWireFormat should write exactly 2 bytes");

        // Verify little-endian encoding (0x1234 -> 0x34 0x12)
        assertEquals((byte) 0x34, buf[0], "First byte should be low byte of level");