Testing – Modifying Block Number with Hardhat

hardhattesting

I see that is it is possible to define the timestamp of the next block (see here) in this way:

await network.provider.send("evm_setNextBlockTimestamp", [1625097600]);
await network.provider.send("evm_mine");

but what about setting the block number?

My contracts use block.number to perform operations and I need to verify that they act correctly by mining a block with a greater height.

Best Answer

I ended up modifying the block.number by mining multiple blocks as it was suggested in the comment by Franco Victorio.

This is the code:

async function mineNBlocks(n) {
  for (let index = 0; index < n; index++) {
    await ethers.provider.send('evm_mine');
  }
}

Then it is called with:

await mineNBlocks(750);

It was a bit slow, but it worked quite well for what I needed it.

Related Solutions

[Ethereum] Geth Console – Sleep after mining a block

You can write a JavaScript script that controls geth's behavior related to mining.

There is a simple script that mines only nonempty blocks on go-ethereum wiki. Another one is mine.js script from Embark Framework. This one is feature-rich and configurable for periodic mining, mining reward cap, number of mining threads and more (via glider).

Scripts are loaded with js command, for example:

geth --rpc js mining.js

Hardhat Testing – How to Interact with the Functions of Smart Contract in Hardhat

Basically, you need to deploy the contract to your local hardhat net just as you would to any other. That means currently you have to set up a deploy.js like in the official hardhat tutorial. I'm assuming you followed the official tutorial at least until Chapter 7: Deploying to a live network and e.g. @nomiclabs/hardhat-ethers is already properly installed.

Preparations

❶ Run:

npx hardhat node

❷ Open a new console window at your project directory. Deploy your smart contract by using the previously mentioned deploy.js. You need the --network parameter to specify that you want to deploy to localhost.

npx hardhat run --network localhost scripts/deploy.js

The script will throw back some useful information. Keep an eye on the second address (designated by the contract's name) – you will need it in Step 4.

❸ Connect to the hardhat console at localhost with:

npx hardhat console --network localhost

❹ Get the ethers.js contract factory and attach to it.

Use the proper name in getContractFactory() and paste the address from step 2 in attach()

const Token = await ethers.getContractFactory("Token")
const token = await Token.attach("0x5FbDB2315678afecb367f032d93F642f64180aa3")

Or in one command:

const token = await (await ethers.getContractFactory("Token")).attach("0x5FbDB2315678afecb367f032d93F642f64180aa3")

Interact with contract

You're in a JavaScript environment. E.g. call the transfer method of the hardhat tutorial. For the complete API, see ethers.js API Docs

Two more tips:

Use await to avoid Promise objects.
.toString() helps you to display uint256 numbers (which are too big for JS).

For a more detailed read, refer to the excellent OpenZeppelin tutorial for hardhat.

> await token.transfer("0xdd2fd4581271e230360230f9337d5c0430bf44c0", 42069)
{
  hash: '0xdc0493ce8ed950b4d4558deb65605ba773067804eacfefd7fc64274a8a805dea',
  ...
> (await token.balanceOf("0xdd2fd4581271e230360230f9337d5c0430bf44c0")).toString()
'42069'