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 web3 import Web3
  6from web3.contract import Contract, mk_collision_prop
  7from web3.providers.eth_tester import EthereumTesterProvider
  8
  9from vyper import compiler
 10
 11from .grammar.conftest import get_lark_grammar
 12
 13LARK_GRAMMAR = get_lark_grammar()
 14
 15
 16class VyperMethod:
 17    ALLOWED_MODIFIERS = {"call", "estimateGas", "transact", "buildTransaction"}
 18
 19    def __init__(self, function, normalizers=None):
 20        self._function = function
 21        self._function._return_data_normalizers = normalizers
 22
 23    def __call__(self, *args, **kwargs):
 24        return self.__prepared_function(*args, **kwargs)
 25
 26    def __prepared_function(self, *args, **kwargs):
 27        if not kwargs:
 28            modifier, modifier_dict = "call", {}
 29            fn_abi = [
 30                x
 31                for x in self._function.contract_abi
 32                if x.get("name") == self._function.function_identifier
 33            ].pop()
 34            # To make tests faster just supply some high gas value.
 35            modifier_dict.update({"gas": fn_abi.get("gas", 0) + 50000})
 36        elif len(kwargs) == 1:
 37            modifier, modifier_dict = kwargs.popitem()
 38            if modifier not in self.ALLOWED_MODIFIERS:
 39                raise TypeError(f"The only allowed keyword arguments are: {self.ALLOWED_MODIFIERS}")
 40        else:
 41            raise TypeError(f"Use up to one keyword argument, one of: {self.ALLOWED_MODIFIERS}")
 42        return getattr(self._function(*args), modifier)(modifier_dict)
 43
 44
 45class VyperContract:
 46    """
 47    An alternative Contract Factory which invokes all methods as `call()`,
 48    unless you add a keyword argument. The keyword argument assigns the prep method.
 49    This call
 50    > contract.withdraw(amount, transact={'from': eth.accounts[1], 'gas': 100000, ...})
 51    is equivalent to this call in the classic contract:
 52    > contract.functions.withdraw(amount).transact({'from': eth.accounts[1], 'gas': 100000, ...})
 53    """
 54
 55    def __init__(self, classic_contract, method_class=VyperMethod):
 56        classic_contract._return_data_normalizers += CONCISE_NORMALIZERS
 57        self._classic_contract = classic_contract
 58        self.address = self._classic_contract.address
 59        protected_fn_names = [fn for fn in dir(self) if not fn.endswith("__")]
 60        for fn_name in self._classic_contract.functions:
 61            # Override namespace collisions
 62            if fn_name in protected_fn_names:
 63                _concise_method = mk_collision_prop(fn_name)
 64            else:
 65                _classic_method = getattr(self._classic_contract.functions, fn_name)
 66                _concise_method = method_class(
 67                    _classic_method, self._classic_contract._return_data_normalizers
 68                )
 69            setattr(self, fn_name, _concise_method)
 70
 71    @classmethod
 72    def factory(cls, *args, **kwargs):
 73        return compose(cls, Contract.factory(*args, **kwargs))
 74
 75
 76def _none_addr(datatype, data):
 77    if datatype == "address" and int(data, base=16) == 0:
 78        return (datatype, None)
 79    else:
 80        return (datatype, data)
 81
 82
 83CONCISE_NORMALIZERS = (_none_addr,)
 84
 85
 86@pytest.fixture(scope="module")
 87def tester():
 88    # set absurdly high gas limit so that london basefee never adjusts
 89    # (note: 2**63 - 1 is max that evm allows)
 90    custom_genesis = PyEVMBackend._generate_genesis_params(overrides={"gas_limit": 10 ** 10})
 91    custom_genesis["base_fee_per_gas"] = 0
 92    backend = PyEVMBackend(genesis_parameters=custom_genesis)
 93    return EthereumTester(backend=backend)
 94
 95
 96def zero_gas_price_strategy(web3, transaction_params=None):
 97    return 0  # zero gas price makes testing simpler.
 98
 99
100@pytest.fixture(scope="module")
101def w3(tester):
102    w3 = Web3(EthereumTesterProvider(tester))
103    w3.eth.set_gas_price_strategy(zero_gas_price_strategy)
104    return w3
105
106
107def _get_contract(w3, source_code, no_optimize, *args, **kwargs):
108    out = compiler.compile_code(
109        source_code,
110        ["abi", "bytecode"],
111        interface_codes=kwargs.pop("interface_codes", None),
112        no_optimize=no_optimize,
113        evm_version=kwargs.pop("evm_version", None),
114        show_gas_estimates=True,  # Enable gas estimates for testing
115    )
116    LARK_GRAMMAR.parse(source_code + "\n")  # Test grammar.
117    abi = out["abi"]
118    bytecode = out["bytecode"]
119    value = kwargs.pop("value_in_eth", 0) * 10 ** 18  # Handle deploying with an eth value.
120    c = w3.eth.contract(abi=abi, bytecode=bytecode)
121    deploy_transaction = c.constructor(*args)
122    tx_info = {
123        "from": w3.eth.accounts[0],
124        "value": value,
125        "gasPrice": 0,
126    }
127    tx_info.update(kwargs)
128    tx_hash = deploy_transaction.transact(tx_info)
129    address = w3.eth.get_transaction_receipt(tx_hash)["contractAddress"]
130    return w3.eth.contract(
131        address,
132        abi=abi,
133        bytecode=bytecode,
134        ContractFactoryClass=VyperContract,
135    )
136
137
138@pytest.fixture(scope="module")
139def get_contract(w3, no_optimize):
140    def get_contract(source_code, *args, **kwargs):
141        return _get_contract(w3, source_code, no_optimize, *args, **kwargs)
142
143    return get_contract
144
145
146@pytest.fixture
147def get_logs(w3):
148    def get_logs(tx_hash, c, event_name):
149        tx_receipt = w3.eth.get_transaction_receipt(tx_hash)
150        return c._classic_contract.events[event_name]().processReceipt(tx_receipt)
151
152    return get_logs
153
154
155@pytest.fixture(scope="module")
156def assert_tx_failed(tester):
157    def assert_tx_failed(function_to_test, exception=TransactionFailed, exc_text=None):
158        snapshot_id = tester.take_snapshot()
159        with pytest.raises(exception) as excinfo:
160            function_to_test()
161        tester.revert_to_snapshot(snapshot_id)
162        if exc_text:
163            # TODO test equality
164            assert exc_text in str(excinfo.value), (exc_text, excinfo.value)
165
166    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