Testing with Ethereum Tester

Ethereum Tester is a tool suite for testing Ethereum based applications.

This section provides a quick overview of testing with eth-tester. To learn more, you can view the documentation at the Github repo or join the Gitter channel.

Getting Started

Prior to testing, the Vyper specific contract conversion and the blockchain related fixtures need to be set up. These fixtures will be used in every test file and should therefore be defined in conftest.py.

Note

Since the testing is done in the pytest framework, you can make use of pytest.ini, tox.ini and setup.cfg and you can use most IDEs’ pytest plugins.

  1import json
  2
  3import pytest
  4import web3.exceptions
  5from eth_tester import EthereumTester, PyEVMBackend
  6from eth_tester.exceptions import TransactionFailed
  7from eth_utils.toolz import compose
  8from hexbytes import HexBytes
  9from web3 import Web3
 10from web3.contract import Contract
 11from web3.providers.eth_tester import EthereumTesterProvider
 12
 13from vyper import compiler
 14from vyper.ast.grammar import parse_vyper_source
 15
 16
 17class VyperMethod:
 18    ALLOWED_MODIFIERS = {"call", "estimateGas", "transact", "buildTransaction"}
 19
 20    def __init__(self, function, normalizers=None):
 21        self._function = function
 22        self._function._return_data_normalizers = normalizers
 23
 24    def __call__(self, *args, **kwargs):
 25        return self.__prepared_function(*args, **kwargs)
 26
 27    def __prepared_function(self, *args, **kwargs):
 28        if not kwargs:
 29            modifier, modifier_dict = "call", {}
 30            fn_abi = [
 31                x
 32                for x in self._function.contract_abi
 33                if x.get("name") == self._function.function_identifier
 34            ].pop()
 35            # To make tests faster just supply some high gas value.
 36            modifier_dict.update({"gas": fn_abi.get("gas", 0) + 500000})
 37        elif len(kwargs) == 1:
 38            modifier, modifier_dict = kwargs.popitem()
 39            if modifier not in self.ALLOWED_MODIFIERS:
 40                raise TypeError(f"The only allowed keyword arguments are: {self.ALLOWED_MODIFIERS}")
 41        else:
 42            raise TypeError(f"Use up to one keyword argument, one of: {self.ALLOWED_MODIFIERS}")
 43        return getattr(self._function(*args), modifier)(modifier_dict)
 44
 45
 46class VyperContract:
 47    """
 48    An alternative Contract Factory which invokes all methods as `call()`,
 49    unless you add a keyword argument. The keyword argument assigns the prep method.
 50    This call
 51    > contract.withdraw(amount, transact={'from': eth.accounts[1], 'gas': 100000, ...})
 52    is equivalent to this call in the classic contract:
 53    > contract.functions.withdraw(amount).transact({'from': eth.accounts[1], 'gas': 100000, ...})
 54    """
 55
 56    def __init__(self, classic_contract, method_class=VyperMethod):
 57        classic_contract._return_data_normalizers += CONCISE_NORMALIZERS
 58        self._classic_contract = classic_contract
 59        self.address = self._classic_contract.address
 60        protected_fn_names = [fn for fn in dir(self) if not fn.endswith("__")]
 61
 62        try:
 63            fn_names = [fn["name"] for fn in self._classic_contract.functions._functions]
 64        except web3.exceptions.NoABIFunctionsFound:
 65            fn_names = []
 66
 67        for fn_name in fn_names:
 68            # Override namespace collisions
 69            if fn_name in protected_fn_names:
 70                raise AttributeError(f"{fn_name} is protected!")
 71            else:
 72                _classic_method = getattr(self._classic_contract.functions, fn_name)
 73                _concise_method = method_class(
 74                    _classic_method, self._classic_contract._return_data_normalizers
 75                )
 76            setattr(self, fn_name, _concise_method)
 77
 78    @classmethod
 79    def factory(cls, *args, **kwargs):
 80        return compose(cls, Contract.factory(*args, **kwargs))
 81
 82
 83def _none_addr(datatype, data):
 84    if datatype == "address" and int(data, base=16) == 0:
 85        return (datatype, None)
 86    else:
 87        return (datatype, data)
 88
 89
 90CONCISE_NORMALIZERS = (_none_addr,)
 91
 92
 93@pytest.fixture(scope="module")
 94def tester():
 95    # set absurdly high gas limit so that london basefee never adjusts
 96    # (note: 2**63 - 1 is max that evm allows)
 97    custom_genesis = PyEVMBackend._generate_genesis_params(overrides={"gas_limit": 10**10})
 98    custom_genesis["base_fee_per_gas"] = 0
 99    backend = PyEVMBackend(genesis_parameters=custom_genesis)
100    return EthereumTester(backend=backend)
101
102
103def zero_gas_price_strategy(web3, transaction_params=None):
104    return 0  # zero gas price makes testing simpler.
105
106
107@pytest.fixture(scope="module")
108def w3(tester):
109    w3 = Web3(EthereumTesterProvider(tester))
110    w3.eth.set_gas_price_strategy(zero_gas_price_strategy)
111    return w3
112
113
114def _get_contract(w3, source_code, no_optimize, *args, **kwargs):
115    out = compiler.compile_code(
116        source_code,
117        # test that metadata gets generated
118        ["abi", "bytecode", "metadata"],
119        interface_codes=kwargs.pop("interface_codes", None),
120        no_optimize=no_optimize,
121        evm_version=kwargs.pop("evm_version", None),
122        show_gas_estimates=True,  # Enable gas estimates for testing
123    )
124    parse_vyper_source(source_code)  # Test grammar.
125    json.dumps(out["metadata"])  # test metadata is json serializable
126    abi = out["abi"]
127    bytecode = out["bytecode"]
128    value = kwargs.pop("value_in_eth", 0) * 10**18  # Handle deploying with an eth value.
129    c = w3.eth.contract(abi=abi, bytecode=bytecode)
130    deploy_transaction = c.constructor(*args)
131    tx_info = {"from": w3.eth.accounts[0], "value": value, "gasPrice": 0}
132    tx_info.update(kwargs)
133    tx_hash = deploy_transaction.transact(tx_info)
134    address = w3.eth.get_transaction_receipt(tx_hash)["contractAddress"]
135    return w3.eth.contract(address, abi=abi, bytecode=bytecode, ContractFactoryClass=VyperContract)
136
137
138def _deploy_blueprint_for(w3, source_code, no_optimize, initcode_prefix=b"", **kwargs):
139    out = compiler.compile_code(
140        source_code,
141        ["abi", "bytecode"],
142        interface_codes=kwargs.pop("interface_codes", None),
143        no_optimize=no_optimize,
144        evm_version=kwargs.pop("evm_version", None),
145        show_gas_estimates=True,  # Enable gas estimates for testing
146    )
147    parse_vyper_source(source_code)  # Test grammar.
148    abi = out["abi"]
149    bytecode = HexBytes(initcode_prefix) + HexBytes(out["bytecode"])
150    bytecode_len = len(bytecode)
151    bytecode_len_hex = hex(bytecode_len)[2:].rjust(4, "0")
152    # prepend a quick deploy preamble
153    deploy_preamble = HexBytes("61" + bytecode_len_hex + "3d81600a3d39f3")
154    deploy_bytecode = HexBytes(deploy_preamble) + bytecode
155
156    deployer_abi = []  # just a constructor
157    c = w3.eth.contract(abi=deployer_abi, bytecode=deploy_bytecode)
158    deploy_transaction = c.constructor()
159    tx_info = {"from": w3.eth.accounts[0], "value": 0, "gasPrice": 0}
160
161    tx_hash = deploy_transaction.transact(tx_info)
162    address = w3.eth.get_transaction_receipt(tx_hash)["contractAddress"]
163
164    # sanity check
165    assert w3.eth.get_code(address) == bytecode, (w3.eth.get_code(address), bytecode)
166
167    def factory(address):
168        return w3.eth.contract(
169            address, abi=abi, bytecode=bytecode, ContractFactoryClass=VyperContract
170        )
171
172    return w3.eth.contract(address, bytecode=deploy_bytecode), factory
173
174
175@pytest.fixture(scope="module")
176def deploy_blueprint_for(w3, no_optimize):
177    def deploy_blueprint_for(source_code, *args, **kwargs):
178        return _deploy_blueprint_for(w3, source_code, no_optimize, *args, **kwargs)
179
180    return deploy_blueprint_for
181
182
183@pytest.fixture(scope="module")
184def get_contract(w3, no_optimize):
185    def get_contract(source_code, *args, **kwargs):
186        return _get_contract(w3, source_code, no_optimize, *args, **kwargs)
187
188    return get_contract
189
190
191@pytest.fixture
192def get_logs(w3):
193    def get_logs(tx_hash, c, event_name):
194        tx_receipt = w3.eth.get_transaction_receipt(tx_hash)
195        return c._classic_contract.events[event_name]().process_receipt(tx_receipt)
196
197    return get_logs
198
199
200@pytest.fixture(scope="module")
201def assert_tx_failed(tester):
202    def assert_tx_failed(function_to_test, exception=TransactionFailed, exc_text=None):
203        snapshot_id = tester.take_snapshot()
204        with pytest.raises(exception) as excinfo:
205            function_to_test()
206        tester.revert_to_snapshot(snapshot_id)
207        if exc_text:
208            # TODO test equality
209            assert exc_text in str(excinfo.value), (exc_text, excinfo.value)
210
211    return assert_tx_failed

The final two fixtures are optional and will be discussed later. The rest of this chapter assumes that you have this code set up in your conftest.py file.

Alternatively, you can import the fixtures to conftest.py or use pytest plugins.

Writing a Basic Test

Assume the following simple contract storage.vy. It has a single integer variable and a function to set that value.

1storedData: public(int128)
2
3@external
4def __init__(_x: int128):
5  self.storedData = _x
6
7@external
8def set(_x: int128):
9  self.storedData = _x

We create a test file test_storage.py where we write our tests in pytest style.

 1import pytest
 2
 3INITIAL_VALUE = 4
 4
 5
 6@pytest.fixture
 7def storage_contract(w3, get_contract):
 8    with open("examples/storage/storage.vy") as f:
 9        contract_code = f.read()
10        # Pass constructor variables directly to the contract
11        contract = get_contract(contract_code, INITIAL_VALUE)
12    return contract
13
14
15def test_initial_state(storage_contract):
16    # Check if the constructor of the contract is set up properly
17    assert storage_contract.storedData() == INITIAL_VALUE
18
19
20def test_set(w3, storage_contract):
21    k0 = w3.eth.accounts[0]
22
23    # Let k0 try to set the value to 10
24    storage_contract.set(10, transact={"from": k0})
25    assert storage_contract.storedData() == 10  # Directly access storedData
26
27    # Let k0 try to set the value to -5
28    storage_contract.set(-5, transact={"from": k0})
29    assert storage_contract.storedData() == -5

First we create a fixture for the contract which will compile our contract and set up a Web3 contract object. We then use this fixture for our test functions to interact with the contract.

Note

To run the tests, call pytest or python -m pytest from your project directory.

Events and Failed Transactions

To test events and failed transactions we expand our simple storage contract to include an event and two conditions for a failed transaction: advanced_storage.vy

 1event DataChange:
 2    setter: indexed(address)
 3    value: int128
 4
 5storedData: public(int128)
 6
 7@external
 8def __init__(_x: int128):
 9  self.storedData = _x
10
11@external
12def set(_x: int128):
13  assert _x >= 0, "No negative values"
14  assert self.storedData < 100, "Storage is locked when 100 or more is stored"
15  self.storedData = _x
16  log DataChange(msg.sender, _x)
17
18@external
19def reset():
20  self.storedData = 0

Next, we take a look at the two fixtures that will allow us to read the event logs and to check for failed transactions.

@pytest.fixture(scope="module")
def assert_tx_failed(tester):
    def assert_tx_failed(function_to_test, exception=TransactionFailed, exc_text=None):
        snapshot_id = tester.take_snapshot()
        with pytest.raises(exception) as excinfo:
            function_to_test()
        tester.revert_to_snapshot(snapshot_id)
        if exc_text:
            # TODO test equality
            assert exc_text in str(excinfo.value), (exc_text, excinfo.value)

    return assert_tx_failed

The fixture to assert failed transactions defaults to check for a TransactionFailed exception, but can be used to check for different exceptions too, as shown below. Also note that the chain gets reverted to the state before the failed transaction.

@pytest.fixture
def get_logs(w3):
    def get_logs(tx_hash, c, event_name):
        tx_receipt = w3.eth.get_transaction_receipt(tx_hash)
        return c._classic_contract.events[event_name]().process_receipt(tx_receipt)

    return get_logs

This fixture will return a tuple with all the logs for a certain event and transaction. The length of the tuple equals the number of events (of the specified type) logged and should be checked first.

Finally, we create a new file test_advanced_storage.py where we use the new fixtures to test failed transactions and events.

 1import pytest
 2from web3.exceptions import ValidationError
 3
 4INITIAL_VALUE = 4
 5
 6
 7@pytest.fixture
 8def adv_storage_contract(w3, get_contract):
 9    with open("examples/storage/advanced_storage.vy") as f:
10        contract_code = f.read()
11        # Pass constructor variables directly to the contract
12        contract = get_contract(contract_code, INITIAL_VALUE)
13    return contract
14
15
16def test_initial_state(adv_storage_contract):
17    # Check if the constructor of the contract is set up properly
18    assert adv_storage_contract.storedData() == INITIAL_VALUE
19
20
21def test_failed_transactions(w3, adv_storage_contract, assert_tx_failed):
22    k1 = w3.eth.accounts[1]
23
24    # Try to set the storage to a negative amount
25    assert_tx_failed(lambda: adv_storage_contract.set(-10, transact={"from": k1}))
26
27    # Lock the contract by storing more than 100. Then try to change the value
28    adv_storage_contract.set(150, transact={"from": k1})
29    assert_tx_failed(lambda: adv_storage_contract.set(10, transact={"from": k1}))
30
31    # Reset the contract and try to change the value
32    adv_storage_contract.reset(transact={"from": k1})
33    adv_storage_contract.set(10, transact={"from": k1})
34    assert adv_storage_contract.storedData() == 10
35
36    # Assert a different exception (ValidationError for non matching argument type)
37    assert_tx_failed(
38        lambda: adv_storage_contract.set("foo", transact={"from": k1}), ValidationError
39    )
40
41    # Assert a different exception that contains specific text
42    assert_tx_failed(
43        lambda: adv_storage_contract.set(1, 2, transact={"from": k1}),
44        ValidationError,
45        "invocation failed due to improper number of arguments",
46    )
47
48
49def test_events(w3, adv_storage_contract, get_logs):
50    k1, k2 = w3.eth.accounts[:2]
51
52    tx1 = adv_storage_contract.set(10, transact={"from": k1})
53    tx2 = adv_storage_contract.set(20, transact={"from": k2})
54    tx3 = adv_storage_contract.reset(transact={"from": k1})
55
56    # Save DataChange logs from all three transactions
57    logs1 = get_logs(tx1, adv_storage_contract, "DataChange")
58    logs2 = get_logs(tx2, adv_storage_contract, "DataChange")
59    logs3 = get_logs(tx3, adv_storage_contract, "DataChange")
60
61    # Check log contents
62    assert len(logs1) == 1
63    assert logs1[0].args.value == 10
64
65    assert len(logs2) == 1
66    assert logs2[0].args.setter == k2
67
68    assert not logs3  # tx3 does not generate a log