static Path buildLockFilePath(final ContentPackZip contentPackZip, final Path destDir) {
        final String filename = contentPackZip.toFileName();
        return destDir.resolve(filename + ".lock");
    }
synchronized to avoid multiple test threads downloading the same pack concurrently
Don't have to worry about other JVM as this method is called under lock on a single common file.
stroom-test-common/src/main/java/stroom/test/common/util/test/ContentPackZipDownloader.java