Dev mode

Geth has a development mode which sets up a single node Ethereum test network with a number of options optimized for developing on local machines. You enable it with the --dev argument.

Starting geth in dev mode does the following:

• Initializes the data directory with a testing genesis block
• Sets max peers to 0
• Turns off discovery by other nodes
• Sets the gas price to 0
• Uses the Clique PoA consensus engine with which allows blocks to be mined as-needed without excessive CPU and memory consumption
• Uses on-demand block generation, producing blocks when there are transactions waiting to be mined

You can specify a data directory to maintain state between runs using the --datadir option, otherwise databases are ephemeral and in-memory:

$ mkdir test-chain-dir
$ geth --dev --datadir test-chain-dir console

Once geth is running in dev mode, you can interact with it in the same way as when geth is running in other ways.

For example, create a test account:

> personal.newAccount()

Then transfer ether from the coinbase to the new account:

> eth.sendTransaction({from:eth.coinbase, to:eth.accounts[1], value: web3.toWei(0.05, "ether")})

And check the balance of the account:

> eth.getBalance(eth.accounts[1])

If you want to test your dapps with a realistic block time use the --dev.period option when you start dev mode:

geth --dev --dev.period 14 console