Who's mining the testnet?

[fbueller]

What's going on over in the testnet? Someone's mining like crazy the past few days. https://blockexplorer.com/testnet at the moment shows someone mining about 13 blocks every two minutes. Is it for a faucet, or what?

It's kind of annoying, the bitcoind script I have displays output with each block. I'm curious what people think of this

EDIT: Maybe someone is doing this.. https://bitcointalk.org/?topic=4483.0

[jgarzik]

It's annoying.

If it continues for too long, we will have to reset testnet to a new genesis block, which is a pain.

ASIC miners should test with Testnet-In-A-Box.  http://sourceforge.net/projects/bitcoin/files/Bitcoin/testnet-in-a-box/

[fbueller]

Interesting. I thought it was strange behavior to see alright, I normally never get much output from that script.

Is the genesis block (for testnet and real network) hard coded into a client or has the client to be activated? Curious if this would require an upgrade now!

[jgarzik]

Yes, the genesis block is hardcoded into the client.

[pocesar]

I was just going to post about this... what can be done? I don't have an ASIC and need to use testnet using a CPU for testing purposes, but having to wait 10 minutes for the test to accomplish is a pain.

[Mike Hearn]

We need developer documentation on bitcoin.org

The right way to test apps locally these days is not to use the testnet at all. Instead build from git master and use regression test mode. It has (yet another) genesis block and set of parameters, however, in regtest mode:

1) Difficulty is set so low a new block can be mined on a CPU instantly.

2) The "bitcoind -regtest setgenerate true" command will mine a single block and then stop.

This means that if you connect your app to a local regtest mode node, you can get a block whenever you want, only when you want, without having to wait.

If you combine this feature with the blacklist block RPC that Pieter Wiulle has put in a github pull req, you can also trigger arbitrary re-orgs whenever you like, which is great for testing that your app behaves correctly in the presence of re-orgs (otherwise this is hard to test properly).

[deepceleron]

A feature of testnet could be used as a difficulty-amplification attack. I've just done it for fun and profit.

"In addition, if no block has been found in 20 minutes, the difficulty automatically resets back to the minimum for a single block, after which it returns to its previous value."

while the last block was full difficulty:
 while the local time isn't more than two hours ahead of network time
  Set local clock forward 20 minutes from last block,
  mine difficulty 1 block,

This could drive difficulty seven times higher than actual hashrate.

On the plus side, easy 50 BTC if you can't ASIC mine. I made the same 300 testBTC in 5 minutes as I did in two days of GPU.

One for the bug pile: getmininginfo displays the last block's difficulty, not the targeted difficulty. On testnet it will often display "difficulty: 1" from this keep-blocks-a-rollin' feature.

[jgarzik]

There are possible attacks on testnet difficulty.  The resolution is the same:  if it becomes unusable, reset the genesis block, and start testnet4.

Part of the "testnet contract" is that it may be reset.