A newbie here, just trying to connect the dots.
Why are there so many test environments in the ethereum ecosystem -- rinkebys, testrpc, ropsten and what else? Why not have just one testing environment that is as close to the "state" of the real production i.e. mainnet as possible?
What's the reasoning behind it?
Initially there was a single test network which used proof of work same as the main network. It turned out that it's vulnerable to DoS attacks, because the difficulty of mining is very low - anyone with enough computing power can mine blocks with lots of spammy transactions. Ropsten testnet is under kind of attack? What can we do?
As a solution the Parity team came up with the proof of authority (PoA) algorithm where Ether supply is controlled by trusted parties. The Kovan testnet uses PoA and thus immune to spam attacks. https://github.com/kovan-testnet/proposal
The Ethereum team then came up with their own PoA algorithm and rolled out the Rinkeby testnet: https://github.com/ethereum/EIPs/issues/225
You can find more details in this answer Comparison of the different TestNets
testRPC (or Ganache nowadays) is a tool running locally (or on virtual machine) to test your application on private blockchain. It is not a separate public test network. It can be configured to meet any particular needs of development and testing.
