Fork Testing

snforge supports testing in a forked environment. Each test can fork the state of a specified real network and perform actions on top of it.

📝 Note

Actions are performed on top of the forked state which means real network is not affected.

Fork Configuration

There are two ways of configuring a fork:

  • by specifying url and block_id parameters in the #[fork(...)] attribute
  • or by passing a fork name defined in your Scarb.toml to the #[fork(...)] attribute

Configure a Fork in the Attribute

It is possible to pass url and block_id arguments to the fork attribute:

  • url - RPC URL (short string)
  • block_id - id of block which will be pin to fork (BlockId enum)
enum BlockId {
    Tag: BlockTag,
    Hash: felt252,
    Number: u64,

enum BlockTag {
use snforge_std::BlockId;

#[fork(url: "http://your.rpc.url", block_id: BlockId::Number(123))]
fn test_using_forked_state() {
    // ...

Once such a configuration is passed, it is possible to use state and contracts defined on the specified network.

Configure Fork in Scarb.toml

Although passing named arguments works fine, you have to copy-paste it each time you want to use the same fork in tests.

snforge solves this issue by allowing fork configuration inside the Scarb.toml file.

name = "SOME_NAME"
url = "http://your.rpc.url"
block_id.tag = "Latest"

url = "http://your.second.rpc.url"
block_id.number = "123"

url = "http://your.third.rpc.url"
block_id.hash = "0x123"

From this moment forks can be set using their name in the fork attribute.

fn test_using_first_fork() {
    // ...

fn test_using_second_fork() {
    // ...

// ...

Testing Forked Contracts

Once the fork is configured, the test will run on top of the forked state, meaning that it will have access to every contract deployed on the real network.

With that, you can now interact with any contract from the chain the same way you would in a standard test.

⚠️ Warning

The following cheatcodes won't work for forked contracts written in Cairo 0:

  • start_spoof / stop_spoof
  • spy_events