The ModuleKit comes with a some additional utilities to help you test your modules and ensure that they behave as expected.

Gas Calulations

The ModuleKit comes with a gas testing helper library to test gas consumption of UserOps, including for the different phases of the ERC-4337 flow and L2-L1 calldata gas.


Before using this utility, create a folder called gas_calculations in the root folder of the directory (same level as the src folder) and ensure that you have the right permissions settings set in your foundry.toml file:

fs_permissions = [{ access = "read-write", path = "gas_calculations" }]


In order to use the gas testing utility, follow the steps below:

  1. In the test function(s) that you want to perform, call instance.log4337Gas("identifier") before a UserOperation is executed. This will log the gas used for the UserOperation and use the identifier as the filename for the gas report. Make sure to use a unique identifier for each UserOp, otherwise the gas reports will be overwritten.

  2. Execute your tests and add GAS=true to the start of the command. For example: GAS=true forge test.

  3. After the tests have finished, the gas reports will be written to the gas_calculations folder in the root of the project. A gas report will look like this:

  "Calldata": {
    "Arbitrum": "6504 gas",
    "OP-Stack": "8859 gas"
  "Phases": {
    "Creation": "187170 gas",
    "Execution": "37054 gas",
    "Validation": "35980 gas"
  "Total": "2550948 gas"

Note that if you re-run gas calculations, then the newest number will be added and every value will be followed by a (diff: ...) that shows the difference, in gas units between the calculations.

  1. All numbers are in gas units. To calculate the cost in gwei, follow the instructions below:
  • On L1: multiply the total gas used by the gas price in gwei: totalGasUsed * gasPrice
  • On an L2: multiply the total gas used by the L2 gas price in gwei and then add it to to the result of the relevant L2-L1 gas cost muliplied by the L1 gas cost in gwei: totalGasUsed * l2GasPrice + callDataGasUsed * l1GasPrice

Note: if you are calculating the dollar amount of the gas cost, make sure to use the relevant gwei to usd conversions if the L2 has a different gas token to L1.

ERC-4337 Restrictions

ModuleKit allows you to test whether your modules adhere to the ERC-4337 restrictions. These restrictions only apply to the validation phase, so only Validators will need to adhere to them (read more).

In order to simulate these restrictions, simply add SIMULATE=true before your test command. For example: SIMULATE=true forge test. If any of the tests violate any of the ERC-4337 Restrictions, then the ModuleKit will throw an error and describe which restriction has been violated.

Note that we do not yet test the banned opcodes restrictions, but we will add this feature soon.