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_blueprint_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_blueprint_for(w3, no_optimize):
169 def deploy_blueprint_for(source_code, *args, **kwargs):
170 return _deploy_blueprint_for(w3, source_code, no_optimize, *args, **kwargs)
171
172 return deploy_blueprint_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