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
15from vyper.compiler.settings import Settings
16
17
18class VyperMethod:
19 ALLOWED_MODIFIERS = {"call", "estimateGas", "transact", "buildTransaction"}
20
21 def __init__(self, function, normalizers=None):
22 self._function = function
23 self._function._return_data_normalizers = normalizers
24
25 def __call__(self, *args, **kwargs):
26 return self.__prepared_function(*args, **kwargs)
27
28 def __prepared_function(self, *args, **kwargs):
29 if not kwargs:
30 modifier, modifier_dict = "call", {}
31 fn_abi = [
32 x
33 for x in self._function.contract_abi
34 if x.get("name") == self._function.function_identifier
35 ].pop()
36 # To make tests faster just supply some high gas value.
37 modifier_dict.update({"gas": fn_abi.get("gas", 0) + 500000})
38 elif len(kwargs) == 1:
39 modifier, modifier_dict = kwargs.popitem()
40 if modifier not in self.ALLOWED_MODIFIERS:
41 raise TypeError(f"The only allowed keyword arguments are: {self.ALLOWED_MODIFIERS}")
42 else:
43 raise TypeError(f"Use up to one keyword argument, one of: {self.ALLOWED_MODIFIERS}")
44 return getattr(self._function(*args), modifier)(modifier_dict)
45
46
47class VyperContract:
48 """
49 An alternative Contract Factory which invokes all methods as `call()`,
50 unless you add a keyword argument. The keyword argument assigns the prep method.
51 This call
52 > contract.withdraw(amount, transact={'from': eth.accounts[1], 'gas': 100000, ...})
53 is equivalent to this call in the classic contract:
54 > contract.functions.withdraw(amount).transact({'from': eth.accounts[1], 'gas': 100000, ...})
55 """
56
57 def __init__(self, classic_contract, method_class=VyperMethod):
58 classic_contract._return_data_normalizers += CONCISE_NORMALIZERS
59 self._classic_contract = classic_contract
60 self.address = self._classic_contract.address
61 protected_fn_names = [fn for fn in dir(self) if not fn.endswith("__")]
62
63 try:
64 fn_names = [fn["name"] for fn in self._classic_contract.functions._functions]
65 except web3.exceptions.NoABIFunctionsFound:
66 fn_names = []
67
68 for fn_name in fn_names:
69 # Override namespace collisions
70 if fn_name in protected_fn_names:
71 raise AttributeError(f"{fn_name} is protected!")
72 else:
73 _classic_method = getattr(self._classic_contract.functions, fn_name)
74 _concise_method = method_class(
75 _classic_method, self._classic_contract._return_data_normalizers
76 )
77 setattr(self, fn_name, _concise_method)
78
79 @classmethod
80 def factory(cls, *args, **kwargs):
81 return compose(cls, Contract.factory(*args, **kwargs))
82
83
84def _none_addr(datatype, data):
85 if datatype == "address" and int(data, base=16) == 0:
86 return (datatype, None)
87 else:
88 return (datatype, data)
89
90
91CONCISE_NORMALIZERS = (_none_addr,)
92
93
94@pytest.fixture(scope="module")
95def tester():
96 # set absurdly high gas limit so that london basefee never adjusts
97 # (note: 2**63 - 1 is max that evm allows)
98 custom_genesis = PyEVMBackend._generate_genesis_params(overrides={"gas_limit": 10**10})
99 custom_genesis["base_fee_per_gas"] = 0
100 backend = PyEVMBackend(genesis_parameters=custom_genesis)
101 return EthereumTester(backend=backend)
102
103
104def zero_gas_price_strategy(web3, transaction_params=None):
105 return 0 # zero gas price makes testing simpler.
106
107
108@pytest.fixture(scope="module")
109def w3(tester):
110 w3 = Web3(EthereumTesterProvider(tester))
111 w3.eth.set_gas_price_strategy(zero_gas_price_strategy)
112 return w3
113
114
115def _get_contract(w3, source_code, optimize, *args, override_opt_level=None, **kwargs):
116 settings = Settings()
117 settings.evm_version = kwargs.pop("evm_version", None)
118 settings.optimize = override_opt_level or optimize
119 out = compiler.compile_code(
120 source_code,
121 # test that metadata and natspecs get generated
122 ["abi", "bytecode", "metadata", "userdoc", "devdoc"],
123 settings=settings,
124 interface_codes=kwargs.pop("interface_codes", None),
125 show_gas_estimates=True, # Enable gas estimates for testing
126 )
127 parse_vyper_source(source_code) # Test grammar.
128 json.dumps(out["metadata"]) # test metadata is json serializable
129 abi = out["abi"]
130 bytecode = out["bytecode"]
131 value = kwargs.pop("value_in_eth", 0) * 10**18 # Handle deploying with an eth value.
132 c = w3.eth.contract(abi=abi, bytecode=bytecode)
133 deploy_transaction = c.constructor(*args)
134 tx_info = {"from": w3.eth.accounts[0], "value": value, "gasPrice": 0}
135 tx_info.update(kwargs)
136 tx_hash = deploy_transaction.transact(tx_info)
137 address = w3.eth.get_transaction_receipt(tx_hash)["contractAddress"]
138 return w3.eth.contract(address, abi=abi, bytecode=bytecode, ContractFactoryClass=VyperContract)
139
140
141def _deploy_blueprint_for(w3, source_code, optimize, initcode_prefix=b"", **kwargs):
142 settings = Settings()
143 settings.evm_version = kwargs.pop("evm_version", None)
144 settings.optimize = optimize
145 out = compiler.compile_code(
146 source_code,
147 ["abi", "bytecode"],
148 interface_codes=kwargs.pop("interface_codes", None),
149 settings=settings,
150 show_gas_estimates=True, # Enable gas estimates for testing
151 )
152 parse_vyper_source(source_code) # Test grammar.
153 abi = out["abi"]
154 bytecode = HexBytes(initcode_prefix) + HexBytes(out["bytecode"])
155 bytecode_len = len(bytecode)
156 bytecode_len_hex = hex(bytecode_len)[2:].rjust(4, "0")
157 # prepend a quick deploy preamble
158 deploy_preamble = HexBytes("61" + bytecode_len_hex + "3d81600a3d39f3")
159 deploy_bytecode = HexBytes(deploy_preamble) + bytecode
160
161 deployer_abi = [] # just a constructor
162 c = w3.eth.contract(abi=deployer_abi, bytecode=deploy_bytecode)
163 deploy_transaction = c.constructor()
164 tx_info = {"from": w3.eth.accounts[0], "value": 0, "gasPrice": 0}
165
166 tx_hash = deploy_transaction.transact(tx_info)
167 address = w3.eth.get_transaction_receipt(tx_hash)["contractAddress"]
168
169 # sanity check
170 assert w3.eth.get_code(address) == bytecode, (w3.eth.get_code(address), bytecode)
171
172 def factory(address):
173 return w3.eth.contract(
174 address, abi=abi, bytecode=bytecode, ContractFactoryClass=VyperContract
175 )
176
177 return w3.eth.contract(address, bytecode=deploy_bytecode), factory
178
179
180@pytest.fixture(scope="module")
181def deploy_blueprint_for(w3, optimize):
182 def deploy_blueprint_for(source_code, *args, **kwargs):
183 return _deploy_blueprint_for(w3, source_code, optimize, *args, **kwargs)
184
185 return deploy_blueprint_for
186
187
188@pytest.fixture(scope="module")
189def get_contract(w3, optimize):
190 def get_contract(source_code, *args, **kwargs):
191 return _get_contract(w3, source_code, optimize, *args, **kwargs)
192
193 return get_contract
194
195
196@pytest.fixture
197def get_logs(w3):
198 def get_logs(tx_hash, c, event_name):
199 tx_receipt = w3.eth.get_transaction_receipt(tx_hash)
200 return c._classic_contract.events[event_name]().process_receipt(tx_receipt)
201
202 return get_logs
203
204
205@pytest.fixture(scope="module")
206def assert_tx_failed(tester):
207 def assert_tx_failed(function_to_test, exception=TransactionFailed, exc_text=None):
208 snapshot_id = tester.take_snapshot()
209 with pytest.raises(exception) as excinfo:
210 function_to_test()
211 tester.revert_to_snapshot(snapshot_id)
212 if exc_text:
213 # TODO test equality
214 assert exc_text in str(excinfo.value), (exc_text, excinfo.value)
215
216 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