<executions>
          <execution>
            <id>add-benchmark-sources</id>
            <phase>generate-test-sources</phase>
            <goals><goal>add-test-source</goal></goals>
            <configuration>
              <sources>
                <source>benchmark</source>
              </sources>
            </configuration>
          </execution>
        </executions>
      </plugin>

        if (!source.isEmpty()) {
          return false;
        }
      }
      return true;
    }

    @Override
    public Optional<Long> lengthIfKnown() {
      long result = 0L;
      for (CharSource source : sources) {
        Optional<Long> lengthIfKnown = source.lengthIfKnown();
        if (!lengthIfKnown.isPresent()) {
          return Optional.absent();
        }

   *
   * @param sources the sources to concatenate
   * @return a {@code ByteSource} containing the concatenated data
   * @throws NullPointerException if any of {@code sources} is {@code null}
   * @since 15.0
   */
  public static ByteSource concat(ByteSource... sources) {
    return concat(ImmutableList.copyOf(sources));
  }

  /**

  }

  public void testContentEquals() throws IOException {
    assertTrue(source.contentEquals(source));
    assertTrue(source.wasStreamOpened() && source.wasStreamClosed());

    ByteSource equalSource = new TestByteSource(bytes);
    assertTrue(source.contentEquals(equalSource));
    assertTrue(new TestByteSource(bytes).contentEquals(source));

    assertEquals(STRING.length(), source.copyTo(sink));
    assertTrue(source.wasStreamOpened() && source.wasStreamClosed());
    assertTrue(sink.wasStreamOpened() && sink.wasStreamClosed());

    assertEquals(STRING, sink.getString());
  }

  public void testRead_toString() throws IOException {
    assertEquals(STRING, source.read());
    assertTrue(source.wasStreamOpened() && source.wasStreamClosed());
  }

  <build>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
      </plugin>
      <plugin>
        <artifactId>maven-source-plugin</artifactId>
        <executions>
          <execution>
            <id>attach-test-sources</id>
            <phase>post-integration-test</phase>
            <goals><goal>test-jar</goal></goals>
          </execution>
        </executions>
      </plugin>

  }

  public void testContentEquals() throws IOException {
    assertTrue(source.contentEquals(source));
    assertTrue(source.wasStreamOpened() && source.wasStreamClosed());

    ByteSource equalSource = new TestByteSource(bytes);
    assertTrue(source.contentEquals(equalSource));
    assertTrue(new TestByteSource(bytes).contentEquals(source));

          </excludePackageNames>
          <!-- Ignore some tags that are found in Java 11 sources but not recognized... under -source 8, I think it was? I can no longer reproduce the failure. -->
          <tags>
            <tag>
              <name>apiNote</name>
              <placement>X</placement>
            </tag>

          </excludePackageNames>
          <!-- Ignore some tags that are found in Java 11 sources but not recognized... under -source 8, I think it was? I can no longer reproduce the failure. -->
          <tags>
            <tag>
              <name>apiNote</name>
              <placement>X</placement>
            </tag>

                  <fileset dir="${project.build.directory}/failureaccess-sources">
                    <include name="**/InternalFutureFailureAccess.java" />
                  </fileset>
                </copy>
                <!-- Any manually written supersource should take priority over the original guava source, so we set overwrite=true. -->
                <copy toDir="${project.build.directory}/guava-gwt-sources" overwrite="true">