Introduction to Populus Testing Part of Blockchain Testing

Introduction

The Populus framework provides some python code for testing contracts. Testing in the ethereum blockchain by using the python testing framework “py.test”.

By default tests and run the code of ethereum blockchain which is already saved in computer memory.

The drive for tests get placed in the./tests/ directory in the root of the project. In order for py.test to find your, tests modules(File name) their module name must start with test_.

Test Contracts

For testing the contracts we are specially using populus testing. These contract filenames should match or saved with the name as “Test*.sol” and be located anywhere in the memory of 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 fixtures provided by populus for making testing easy. In order to use a fixture in tests to add an argument with the same name to the signature in the test function.

Project:- Firstly project object is initialized, and then 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

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:- Web3.py instance configure to connect to with the 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:- The contract factory classes for the project. Will be associated with the Web3 instance through the web3 fixture.

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

Accounts:- The web3.eth.accounts property off, related with the web3 fixture

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

One case for the contract which needs to give constructor as an argument. Now provide fixtures for a token contract which requires a constructor argument to set the initial supply.

import
pytest 
@pytest.fixture()
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, use this fixture in the tests, same way use the built-in populus fixtures.

def test_initial_supply(token_contract):

assert token_contract.call().totalSupply() == 1e18