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First Usage of Tenderly APIs in Tests

First Usage of Tenderly APIs in Tests

Create a fresh Fork from code

Let’s fork the Ethereum Mainnet on block number 14386016. To do this, we’ll create a Fork we’ll test on the cloud.

The bare minimum you’d want for your tests is in the following snippet:

// the network and block where Tenderly fork gets created
const forkingPoint = { network_id: '1', block_number: 14386016 };
// an axios instance to make requests to Tenderly, for re-use purposes
const axiosOnTenderly = axios.create({
  baseURL: '',
  headers: {
    'X-Access-Key': process.env.TENDERLY_ACCESS_KEY || '',
    'Content-Type': 'application/json',
const projectUrl = `account/${process.env.TENDERLY_ACCOUNT_SLUG}/project/${process.env.TENDERLY_PROJECT_SLUG}`;
// create the specified fork programmatically in your project
const forkResponse = await`${projectUrl}/fork`, fork);
const forkId =;'Forked with fork id:', forkId);
// create the provider you can use throughout the rest of your test
const provider = new JsonRpcProvider(`${forkId}`);

With the Fork we created programmatically, we get a JSON-RPC URL:${forkId}

We can use it later with the library of our choice.

Tenderly creates 10 test addresses with 100 ETH for testing. Any transaction signing will be done by the 0th address as the default signer.

How to deploy a smart contract on the Fork from test code

Please note that you’ll have to specify the signer provided by the provider representing the Tenderly JSON-RPC provider. This way, the ethers’ contract factory deploys the contract to the Tenderly Fork:

const Greeter = await ethers.getContractFactory(
  provider.getSigner(), // use the provider
const greeter = await Greeter.deploy('Hello, world!');
await greeter.deployed();

Since the deploy call is a transaction in its own right, it’s signed by the default signer (0th address). In effect, the 0th test address is the deployer of the contract. You can do things differently, as we’ll see in a bit.

How to interact with the smart contract

Here we’re using ethers, so the interaction goes the standard way. To interact with the smart contract, i.e. call functions (greet) and send transactions (setGreeting), you can simply call these methods on the greeter contract reference. Any transaction will be signed by the 0th test account Tenderly provides, which is also the owner of the contract:

// asserting to it
expect(await greeter.greet())'Hello, world!');
await(await greeter.setGreeting('Hola, mundo!')).wait();
expect(await greeter.greet())'Hola, mundo!');

How to have a different address sign the transaction

This is also a well-known way to use ethers. When a Fork is created, the response from Tenderly’s POST $project/fork contains a list of created test accounts for that Fork. The list is contained in data.simulation_fork.accounts. It’s a map from the address to the balance of that address. So, you need to obtain the address and ask your provider to give you a corresponding signer object.

This way, it’s possible to make a transaction using an arbitrary signer:

// sign with a specific signer
const testAddresses = Object.keys(;
const anotherSigner = provider.getSigner(testAddresses[2]);
await(await greeter.connect(anotherSigner).setGreeting('Bonjour le monde!')).wait();
expect(await greeter.greet())'Bonjour le monde!');

How to delete a Fork after a successful test

Please delete a Fork after your automated tests are complete if you don’t intend to examine transactions and execution via Tenderly anymore. You can achieve this by doing the following:

await axiosOnTenderly.delete(`${projectUrl}/fork/${forkId}`);

Deleting a Fork removes all contracts deployed to it and all transactions executed against it.