ByteStreams.readFully(newTestStream(10), b, 0, 10);
    assertThat(b).isEqualTo(newPreFilledByteArray(10));

    Arrays.fill(b, (byte) 0);
    ByteStreams.readFully(newTestStream(10), b, 0, 5);
    assertThat(b).isEqualTo(new byte[] {0, 1, 2, 3, 4, 0, 0, 0, 0, 0});
  }

  public void testSkipFully() throws IOException {
    byte[] bytes = newPreFilledByteArray(100);
    skipHelper(0, 0, new ByteArrayInputStream(bytes));

    FileBackedOutputStream out = new FileBackedOutputStream(/* fileThreshold= */ 10);
    ByteSource source = out.asByteSource();

    byte[] chunk1 = newPreFilledByteArray(8); // Below threshold
    byte[] chunk2 = newPreFilledByteArray(5); // Crosses threshold
    byte[] chunk3 = newPreFilledByteArray(20); // More data to file

    out.write(chunk1);
    assertThat(out.getFile()).isNull();

    out.write(chunk2);

    // Source of length 5
    AppendableByteSource source = new AppendableByteSource(newPreFilledByteArray(5));

    // Slice it starting at offset 10.
    ByteSource slice = source.slice(10, 5);

    // Open a stream to the slice.
    InputStream in = slice.openStream();

    // Append 10 more bytes to the source.
    source.append(newPreFilledByteArray(5, 10));

  }

  /** Returns a byte array of length size that has values 0 .. size - 1. */
  static byte[] newPreFilledByteArray(int size) {
    return newPreFilledByteArray(0, size);
  }

  /** Returns a byte array of length size that has values offset .. offset + size - 1. */
  static byte[] newPreFilledByteArray(int offset, int size) {
    byte[] array = new byte[size];
    for (int i = 0; i < size; i++) {

    // Source of length 5
    AppendableByteSource source = new AppendableByteSource(newPreFilledByteArray(5));

    // Slice it starting at offset 10.
    ByteSource slice = source.slice(10, 5);

    // Open a stream to the slice.
    InputStream in = slice.openStream();

    // Append 10 more bytes to the source.
    source.append(newPreFilledByteArray(5, 10));

    assertThat(Files.toString(temp, UTF_16LE)).isEqualTo(I18N);
  }

  public void testWriteBytes() throws IOException {
    File temp = createTempFile();
    byte[] data = newPreFilledByteArray(2000);
    Files.write(data, temp);
    assertThat(Files.toByteArray(temp)).isEqualTo(data);

    assertThrows(NullPointerException.class, () -> Files.write(null, temp));
  }

/**
 * Tests for the default implementations of {@code ByteSink} methods.
 *
 * @author Colin Decker
 */
@NullUnmarked
public class ByteSinkTest extends IoTestCase {

  private final byte[] bytes = newPreFilledByteArray(10000);

  private TestByteSink sink;

  @Override
  protected void setUp() throws Exception {
    sink = new TestByteSink();
  }

  public void testOpenBufferedStream() throws IOException {

/**
 * Tests for the default implementations of {@code ByteSink} methods.
 *
 * @author Colin Decker
 */
@NullUnmarked
public class ByteSinkTest extends IoTestCase {

  private final byte[] bytes = newPreFilledByteArray(10000);

  private TestByteSink sink;

  @Override
  protected void setUp() throws Exception {
    sink = new TestByteSink();
  }

  public void testOpenBufferedStream() throws IOException {