Such a test will favor implementations that have extremely svelte boostrapping, allowing them to immediately begin executing the relevant code and return a result.
I feel a more useful test would be for the relevant string processing code to be run tens to thousands of times within the process itself, so as to diminish the relative importance of boostrap/warmup code and/or runtime optimization performed by VMs. Unless, of course, part of the intent was specifically to measure the impact of the bootstrapping.