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 pytest
  2from eth_tester import EthereumTester, PyEVMBackend
  3from eth_tester.exceptions import TransactionFailed
  4from eth_utils.toolz import compose
  5from hexbytes import HexBytes
  6from web3 import Web3
  7from web3.contract import Contract, mk_collision_prop
  8from web3.providers.eth_tester import EthereumTesterProvider
  9
 10from vyper import compiler
 11
 12from .grammar.conftest import get_lark_grammar
 13
 14LARK_GRAMMAR = get_lark_grammar()
 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) + 50000})
 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        for fn_name in self._classic_contract.functions:
 62            # Override namespace collisions
 63            if fn_name in protected_fn_names:
 64                _concise_method = mk_collision_prop(fn_name)
 65            else:
 66                _classic_method = getattr(self._classic_contract.functions, fn_name)
 67                _concise_method = method_class(
 68                    _classic_method, self._classic_contract._return_data_normalizers
 69                )
 70            setattr(self, fn_name, _concise_method)
 71
 72    @classmethod
 73    def factory(cls, *args, **kwargs):
 74        return compose(cls, Contract.factory(*args, **kwargs))
 75
 76
 77def _none_addr(datatype, data):
 78    if datatype == "address" and int(data, base=16) == 0:
 79        return (datatype, None)
 80    else:
 81        return (datatype, data)
 82
 83
 84CONCISE_NORMALIZERS = (_none_addr,)
 85
 86
 87@pytest.fixture(scope="module")
 88def tester():
 89    # set absurdly high gas limit so that london basefee never adjusts
 90    # (note: 2**63 - 1 is max that evm allows)
 91    custom_genesis = PyEVMBackend._generate_genesis_params(overrides={"gas_limit": 10 ** 10})
 92    custom_genesis["base_fee_per_gas"] = 0
 93    backend = PyEVMBackend(genesis_parameters=custom_genesis)
 94    return EthereumTester(backend=backend)
 95
 96
 97def zero_gas_price_strategy(web3, transaction_params=None):
 98    return 0  # zero gas price makes testing simpler.
 99
100
101@pytest.fixture(scope="module")
102def w3(tester):
103    w3 = Web3(EthereumTesterProvider(tester))
104    w3.eth.set_gas_price_strategy(zero_gas_price_strategy)
105    return w3
106
107
108def _get_contract(w3, source_code, no_optimize, *args, **kwargs):
109    out = compiler.compile_code(
110        source_code,
111        ["abi", "bytecode"],
112        interface_codes=kwargs.pop("interface_codes", None),
113        no_optimize=no_optimize,
114        evm_version=kwargs.pop("evm_version", None),
115        show_gas_estimates=True,  # Enable gas estimates for testing
116    )
117    LARK_GRAMMAR.parse(source_code + "\n")  # Test grammar.
118    abi = out["abi"]
119    bytecode = out["bytecode"]
120    value = kwargs.pop("value_in_eth", 0) * 10 ** 18  # Handle deploying with an eth value.
121    c = w3.eth.contract(abi=abi, bytecode=bytecode)
122    deploy_transaction = c.constructor(*args)
123    tx_info = {"from": w3.eth.accounts[0], "value": value, "gasPrice": 0}
124    tx_info.update(kwargs)
125    tx_hash = deploy_transaction.transact(tx_info)
126    address = w3.eth.get_transaction_receipt(tx_hash)["contractAddress"]
127    return w3.eth.contract(address, abi=abi, bytecode=bytecode, ContractFactoryClass=VyperContract)
128
129
130def _deploy_factory_for(w3, source_code, no_optimize, initcode_prefix=b"", **kwargs):
131    out = compiler.compile_code(
132        source_code,
133        ["abi", "bytecode"],
134        interface_codes=kwargs.pop("interface_codes", None),
135        no_optimize=no_optimize,
136        evm_version=kwargs.pop("evm_version", None),
137        show_gas_estimates=True,  # Enable gas estimates for testing
138    )
139    LARK_GRAMMAR.parse(source_code + "\n")  # Test grammar.
140    abi = out["abi"]
141    bytecode = HexBytes(initcode_prefix) + HexBytes(out["bytecode"])
142    bytecode_len = len(bytecode)
143    bytecode_len_hex = hex(bytecode_len)[2:].rjust(4, "0")
144    # prepend a quick deploy preamble
145    deploy_preamble = HexBytes("61" + bytecode_len_hex + "3d81600a3d39f3")
146    deploy_bytecode = HexBytes(deploy_preamble) + bytecode
147
148    deployer_abi = []  # just a constructor
149    c = w3.eth.contract(abi=deployer_abi, bytecode=deploy_bytecode)
150    deploy_transaction = c.constructor()
151    tx_info = {"from": w3.eth.accounts[0], "value": 0, "gasPrice": 0}
152
153    tx_hash = deploy_transaction.transact(tx_info)
154    address = w3.eth.get_transaction_receipt(tx_hash)["contractAddress"]
155
156    # sanity check
157    assert w3.eth.get_code(address) == bytecode, (w3.eth.get_code(address), bytecode)
158
159    def factory(address):
160        return w3.eth.contract(
161            address, abi=abi, bytecode=bytecode, ContractFactoryClass=VyperContract
162        )
163
164    return w3.eth.contract(address, bytecode=deploy_bytecode), factory
165
166
167@pytest.fixture(scope="module")
168def deploy_factory_for(w3, no_optimize):
169    def deploy_factory_for(source_code, *args, **kwargs):
170        return _deploy_factory_for(w3, source_code, no_optimize, *args, **kwargs)
171
172    return deploy_factory_for
173
174
175@pytest.fixture(scope="module")
176def get_contract(w3, no_optimize):
177    def get_contract(source_code, *args, **kwargs):
178        return _get_contract(w3, source_code, no_optimize, *args, **kwargs)
179
180    return get_contract
181
182
183@pytest.fixture
184def get_logs(w3):
185    def get_logs(tx_hash, c, event_name):
186        tx_receipt = w3.eth.get_transaction_receipt(tx_hash)
187        return c._classic_contract.events[event_name]().processReceipt(tx_receipt)
188
189    return get_logs
190
191
192@pytest.fixture(scope="module")
193def assert_tx_failed(tester):
194    def assert_tx_failed(function_to_test, exception=TransactionFailed, exc_text=None):
195        snapshot_id = tester.take_snapshot()
196        with pytest.raises(exception) as excinfo:
197            function_to_test()
198        tester.revert_to_snapshot(snapshot_id)
199        if exc_text:
200            # TODO test equality
201            assert exc_text in str(excinfo.value), (exc_text, excinfo.value)
202
203    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]().processReceipt(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