The Populus framework provides some powerful utilities for testing your contracts. Testing in Populus is powered by the python testing framework py.test.

By default tests are run against an in-memory ethereum blockchain.

The convention for tests is to place them in the ./tests/ directory in the root of your project. In order for py.test to find your tests modules their module name must start with test_.

Test Contracts

Populus supports writing contracts that are specifically for testing. These contract filenames should match the glob pattern Test*.sol and be located anywhere under your project tests directory ./tests/.

Running Tests With Pytest

To run the full test suite of your project:

$ py.test tests/

Or to run a specific test

$ py.test tests/test_greeter.py

Pytest Fixtures

The test fixtures provided by populus are what make testing easy. In order to use a fixture in your tests all you have to do add an argument with the same name to the signature of your test function.


  • project

The Project object for your project.

This project object is initialised first, and the rest of the fixtures are derived from it.

def test_project_things(project):
    # directory things
    assert project.project_dir == '/path/to/my/project'

    # raw compiled contract access
    assert 'MyContract' in project.compiled_contract_data

How populus finds the project of the project fixture

If no other argument is provided, populus defaults to using the current tests directory. This is true if you run py.test from within the project’s directory, or with a positional argument to this project’s directory, e.g. $ py.test /path/to/my/project/.

If the tests are in a different directory, e.g. $ py.tests /path/to/tests/, you will have to provide the tested project:

  1. With command line argument: $ py.test /path/to/tests/ --populus-project /path/to/my/project/
  2. Or, in a pytest.ini file, with the following entry: populus_project=/path/to/my/project/
  3. Or with an environment variable: PYTEST_POPULUS_PROJECT. E.g., PYTEST_POPULUS_PROJECT=/path/to/my/project/ py.test /path/to/tests/

The precedence order for these different methods of setting the project directory is:

  1. command line
  2. pytest.ini
  3. environment variable


  • chain

A running 'tester' test chain.

def test_greeter(chain):
    greeter, _ = chain.provider.get_or_deploy_contract('Greeter')

    assert greeter.call().greet() == "Hello"

def test_deploying_greeter(chain):
    GreeterFactory = chain.provider.get_contract_factory('Greeter')
    deploy_txn_hash = GreeterFactory.deploy()


  • registrar

Convenience fixture for the chain.registrar property.


  • provider

Convenience fixture for the chain.provider property.


  • web3

Convenience fixture for the chain.provider property. A Web3.py instance configured to connect to chain fixture.

def test_account_balance(web3, chain):
    initial_balance = web3.eth.getBalance(web3.eth.coinbase)
    wallet = chain.get_contract('Wallet')

    withdraw_txn_hash = wallet.transact().withdraw(12345)
    withdraw_txn_receipt = chain.wait.for_receipt(withdraw_txn_hash)
    after_balance = web3.eth.getBalance(web3.eth.coinbase)

    assert after_balance - initial_balance == 1234

Base Contract Factories

  • base_contract_factories

The contract factory classes for your project. These will all be associated with the Web3 instance from the web3 fixture.

def test_wallet_deployment(web3, base_contract_factories):
    WalletFactory = base_contract_factories.Wallet

    deploy_txn_hash = WalletFactory.deploy()


For contracts that have library dependencies, you should use the Chain.get_contract_factory(...) api. The contract factories from the base_contract_factories fixture will not be returned with linked bytecode. The ones from Chain.get_contract_factory() are returned fully linked.


  • accounts

The web3.eth.accounts property off of the web3 fixture

def test_accounts(web3, accounts):
    assert web3.eth.coinbase == accounts[0]

Custom Fixtures

The built in fixtures for accessing contracts are useful for simple contracts, but this is often not sufficient for more complex contracts. In these cases you can create you own fixtures to build on top of the ones provided by Populus.

One common case is a contract that needs to be given constructor arguments. Lets make a fixture for a token contract that requires a constructor argument to set the initial supply.

import pytest

def token_contract(chain):
    TokenFactory = chain.get_contract_factory('Token')
    deploy_txn_hash = TokenFactory.deploy(arguments=[
        1e18,  # initial token supply
    contract_address = chain.wait.for_contract_address(deploy_txn_hash)
    return TokenFactory(address=contract_address)

Now, you can use this fixture in your tests the same way you use the built-in populus fixtures.

def test_initial_supply(token_contract):
    assert token_contract.call().totalSupply() == 1e18