Jsgenesis had linked the total supply of tJOYs to a corresponding pool of fiat currency (USD) held by the company. All testnet participants can redeem their tJOY for USD at any time. Every council period, some amount of $USD is added to the pool in order to roughly maintain the exchange rate of $tJOY, despite continuous issuance (i.e. dilution) used to fund on-chain expenses, such as validation, rewards, etc. A dashboard showing up to date information on $tJOY stats, will be published soon(tm).