assertFalse(writer.closed());
    source.copyTo(writer);
    assertFalse(writer.closed());
  }

  public void testClosesOnErrors_copyingToCharSinkThatThrows() {
    for (TestOption option : EnumSet.of(OPEN_THROWS, WRITE_THROWS, CLOSE_THROWS)) {
      TestCharSource okSource = new TestCharSource(STRING);
      assertThrows(IOException.class, () -> okSource.copyTo(new TestCharSink(option)));

    assertFalse(writer.closed());
    source.copyTo(writer);
    assertFalse(writer.closed());
  }

  public void testClosesOnErrors_copyingToCharSinkThatThrows() {
    for (TestOption option : EnumSet.of(OPEN_THROWS, WRITE_THROWS, CLOSE_THROWS)) {
      TestCharSource okSource = new TestCharSource(STRING);
      assertThrows(IOException.class, () -> okSource.copyTo(new TestCharSink(option)));

      TestCharSource failSource = new TestCharSource(STRING, option);
      TestCharSink okSink = new TestCharSink();
      assertThrows(IOException.class, () -> failSource.copyTo(okSink));
      // ensure writer was closed IF it was opened (depends on implementation whether or not it's
      // opened at all if source.newReader() throws).
      assertTrue(

      TestByteSource failSource = new TestByteSource(new byte[10], option);
      TestByteSink okSink = new TestByteSink();
      assertThrows(IOException.class, () -> failSource.copyTo(okSink));
      // ensure stream was closed IF it was opened (depends on implementation whether or not it's
      // opened at all if source.newInputStream() throws).
      assertTrue(

      TestByteSource failSource = new TestByteSource(new byte[10], option);
      TestByteSink okSink = new TestByteSink();
      assertThrows(IOException.class, () -> failSource.copyTo(okSink));
      // ensure stream was closed IF it was opened (depends on implementation whether or not it's
      // opened at all if source.newInputStream() throws).
      assertTrue(

   *       one with {@link CharSequence#charAt(int)}.
   *   <li>use {@link Appendable#append(CharSequence)} in {@link #copyTo(Appendable)} and {@link
   *       #copyTo(CharSink)}. We know this is correct since strings are immutable and so the length
   *       can't change, and it is faster because many writers and appendables are optimized for

   *       one with {@link CharSequence#charAt(int)}.
   *   <li>use {@link Appendable#append(CharSequence)} in {@link #copyTo(Appendable)} and {@link
   *       #copyTo(CharSink)}. We know this is correct since strings are immutable and so the length
   *       can't change, and it is faster because many writers and appendables are optimized for

    StringBuilder builder = new StringBuilder();

    assertEquals(expected.length(), source.copyTo(builder));

    assertExpectedString(builder.toString());
  }

  public void testCopyTo_charSink() throws IOException {
    TestCharSink sink = new TestCharSink();

    assertEquals(expected.length(), source.copyTo(sink));

    assertExpectedString(sink.getString());
  }

    return concat(ImmutableList.copyOf(sources));
  }

  /**
   * Returns a view of the given byte array as a {@link ByteSource}. To view only a specific range
   * in the array, use {@code ByteSource.wrap(b).slice(offset, length)}.
   *
   * <p>Note that the given byte array may be passed directly to methods on, for example, {@code
   * OutputStream} (when {@code copyTo(OutputStream)} is called on the resulting {@code

     *
     * In this case the current thread is assigned as the upstream reader. We read bytes from
     * upstream and copy them to both the file and to the buffer. Finally we release the upstream
     * reader lock and return the new bytes.
     *
     * ## The file
     *
     * In this case we copy bytes from the file to the [sink].
     *
     * ## The buffer
     *