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);

  }

  /** 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++) {

/**
 * 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 {