public void create(@DelegatesTo(value = DirectoryFixture.class, strategy = Closure.DELEGATE_FIRST)
                     Closure<?> dirSpec) throws IOException {
    callSpec(dirSpec, currentPath);
  }
Basically the same as {@link DirectoryFixture#dir(String, Closure)}, but with the current root as base.
spock-core/src/main/java/spock/util/io/FileSystemFixture.java