recently, I have been looking at something related to Ethernet Fang. There is a question about testing network mining that is not clear, as follows:
 
 
 I use  miner.start ()  to dig mines here, young and old, but when I go to   Ropsten Testnet  , I can find my address, but the number of ETH below is 0. later, I looked it up on the Internet and said that the coins in the test network could only be obtained through some places. For example, here     http://faucet.ropsten.be:3001. Here I am confused by B, what is dug in  miner.start () , I am running in the test network, why can"t I find it through   Ropsten testnet  ? 
 would like to know the great god to explain, thank you 
