@Override
    public String toString() {
      return "Namespace{" +
        "parts=" + parts +
        '}';
    }
Create a new namespace by appending the supplied {@code parts} to the
existing sequence of parts in this namespace.

@return new namespace; never {@code null}
@since 2.4
spock-core/src/main/java/org/spockframework/runtime/extension/IStore.java