Hardhat: How to send multiple transactions to be mined in one block

Question

How to send multiple transactions which will be mined in one block in Hardhat tests?

Answer 1

check the mining behavior here

networks: {
  hardhat: {
    mining: {
      auto: false,
      interval: 5000
    }
  }
}

In this example, automining is disabled and interval mining is set so that a new block is generated every 5 seconds. You can also configure interval mining to generate a new block after a random delay:

Manual mining

You can disable both mining modes like this:

networks: {
  hardhat: {
    mining: {
      auto: false,
      interval: 0
    }
  }
}

This means that no new blocks will be mined by the Hardhat Network, but you can manually mine new blocks using the evm_mine RPC method. This will generate a new block that will include as many pending transactions as possible.

you can also use this plugin to handle the mining modes

block.setAutomine(enabled: boolean)

block.setIntervalMine(interval: number | BigNumber)

Answer 2

I was able to follow the response from @Javier Marchetti and send multiple transactions to be mined in the same block. I manually mined the block using evm_setAutomine and evm_setIntervalMining with interval set to "0" in runtime instead of doing it in the configuration file. Then sent the block mine command using RPC method "evm_mine". Here is the summary code

  await network.provider.send("evm_setAutomine", [false]);
  await network.provider.send("evm_setIntervalMining", [0]);
  // SEND TRANSACTION 1
// SEND TRANSACTION 2
  await network.provider.send("evm_mine");

You can check the block numbers for both transactions by console logging them using hardhat console.sol import to verify the transactions were mined in the same block.

Answer 3

The other answers have provided insight into configurations and methods for mining multiple transactions in a single block. I'd like to extend this by offering an example of:

How to write a Hardhat test that must revert and involves mining multiple transactions in one block?

Utilizing await network.provider.send("evm_mine"); can't be paired with the expect().to.be.revertedWith() statement.

Here's how you can achieve this:

await network.provider.send("evm_setAutomine", [false]);
// SEND TRANSACTION 1
// SEND TRANSACTION 2
await network.provider.send("evm_setAutomine", [true]);
await expect(<SEND TRANSACTION 3>).to.be.revertedWith("Three tx's in the same block");

Returning to auto mine doesn't execute the pending transactions immediately. However, the transactions are executed when the next transaction is dispatched.