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
11from vyper.ast.grammar import parse_vyper_source
12
13
14class VyperMethod:
15 ALLOWED_MODIFIERS = {"call", "estimateGas", "transact", "buildTransaction"}
16
17 def __init__(self, function, normalizers=None):
18 self._function = function
19 self._function._return_data_normalizers = normalizers
20
21 def __call__(self, *args, **kwargs):
22 return self.__prepared_function(*args, **kwargs)
23
24 def __prepared_function(self, *args, **kwargs):
25 if not kwargs:
26 modifier, modifier_dict = "call", {}
27 fn_abi = [
28 x
29 for x in self._function.contract_abi
30 if x.get("name") == self._function.function_identifier
31 ].pop()
32 # To make tests faster just supply some high gas value.
33 modifier_dict.update({"gas": fn_abi.get("gas", 0) + 50000})
34 elif len(kwargs) == 1:
35 modifier, modifier_dict = kwargs.popitem()
36 if modifier not in self.ALLOWED_MODIFIERS:
37 raise TypeError(f"The only allowed keyword arguments are: {self.ALLOWED_MODIFIERS}")
38 else:
39 raise TypeError(f"Use up to one keyword argument, one of: {self.ALLOWED_MODIFIERS}")
40 return getattr(self._function(*args), modifier)(modifier_dict)
41
42
43class VyperContract:
44 """
45 An alternative Contract Factory which invokes all methods as `call()`,
46 unless you add a keyword argument. The keyword argument assigns the prep method.
47 This call
48 > contract.withdraw(amount, transact={'from': eth.accounts[1], 'gas': 100000, ...})
49 is equivalent to this call in the classic contract:
50 > contract.functions.withdraw(amount).transact({'from': eth.accounts[1], 'gas': 100000, ...})
51 """
52
53 def __init__(self, classic_contract, method_class=VyperMethod):
54 classic_contract._return_data_normalizers += CONCISE_NORMALIZERS
55 self._classic_contract = classic_contract
56 self.address = self._classic_contract.address
57 protected_fn_names = [fn for fn in dir(self) if not fn.endswith("__")]
58 for fn_name in self._classic_contract.functions:
59 # Override namespace collisions
60 if fn_name in protected_fn_names:
61 _concise_method = mk_collision_prop(fn_name)
62 else:
63 _classic_method = getattr(self._classic_contract.functions, fn_name)
64 _concise_method = method_class(
65 _classic_method, self._classic_contract._return_data_normalizers
66 )
67 setattr(self, fn_name, _concise_method)
68
69 @classmethod
70 def factory(cls, *args, **kwargs):
71 return compose(cls, Contract.factory(*args, **kwargs))
72
73
74def _none_addr(datatype, data):
75 if datatype == "address" and int(data, base=16) == 0:
76 return (datatype, None)
77 else:
78 return (datatype, data)
79
80
81CONCISE_NORMALIZERS = (_none_addr,)
82
83
84@pytest.fixture(scope="module")
85def tester():
86 # set absurdly high gas limit so that london basefee never adjusts
87 # (note: 2**63 - 1 is max that evm allows)
88 custom_genesis = PyEVMBackend._generate_genesis_params(overrides={"gas_limit": 10 ** 10})
89 custom_genesis["base_fee_per_gas"] = 0
90 backend = PyEVMBackend(genesis_parameters=custom_genesis)
91 return EthereumTester(backend=backend)
92
93
94def zero_gas_price_strategy(web3, transaction_params=None):
95 return 0 # zero gas price makes testing simpler.
96
97
98@pytest.fixture(scope="module")
99def w3(tester):
100 w3 = Web3(EthereumTesterProvider(tester))
101 w3.eth.set_gas_price_strategy(zero_gas_price_strategy)
102 return w3
103
104
105def _get_contract(w3, source_code, no_optimize, *args, **kwargs):
106 out = compiler.compile_code(
107 source_code,
108 ["abi", "bytecode"],
109 interface_codes=kwargs.pop("interface_codes", None),
110 no_optimize=no_optimize,
111 evm_version=kwargs.pop("evm_version", None),
112 show_gas_estimates=True, # Enable gas estimates for testing
113 )
114 parse_vyper_source(source_code) # Test grammar.
115 abi = out["abi"]
116 bytecode = out["bytecode"]
117 value = kwargs.pop("value_in_eth", 0) * 10 ** 18 # Handle deploying with an eth value.
118 c = w3.eth.contract(abi=abi, bytecode=bytecode)
119 deploy_transaction = c.constructor(*args)
120 tx_info = {"from": w3.eth.accounts[0], "value": value, "gasPrice": 0}
121 tx_info.update(kwargs)
122 tx_hash = deploy_transaction.transact(tx_info)
123 address = w3.eth.get_transaction_receipt(tx_hash)["contractAddress"]
124 return w3.eth.contract(address, abi=abi, bytecode=bytecode, ContractFactoryClass=VyperContract)
125
126
127def _deploy_blueprint_for(w3, source_code, no_optimize, initcode_prefix=b"", **kwargs):
128 out = compiler.compile_code(
129 source_code,
130 ["abi", "bytecode"],
131 interface_codes=kwargs.pop("interface_codes", None),
132 no_optimize=no_optimize,
133 evm_version=kwargs.pop("evm_version", None),
134 show_gas_estimates=True, # Enable gas estimates for testing
135 )
136 parse_vyper_source(source_code) # Test grammar.
137 abi = out["abi"]
138 bytecode = HexBytes(initcode_prefix) + HexBytes(out["bytecode"])
139 bytecode_len = len(bytecode)
140 bytecode_len_hex = hex(bytecode_len)[2:].rjust(4, "0")
141 # prepend a quick deploy preamble
142 deploy_preamble = HexBytes("61" + bytecode_len_hex + "3d81600a3d39f3")
143 deploy_bytecode = HexBytes(deploy_preamble) + bytecode
144
145 deployer_abi = [] # just a constructor
146 c = w3.eth.contract(abi=deployer_abi, bytecode=deploy_bytecode)
147 deploy_transaction = c.constructor()
148 tx_info = {"from": w3.eth.accounts[0], "value": 0, "gasPrice": 0}
149
150 tx_hash = deploy_transaction.transact(tx_info)
151 address = w3.eth.get_transaction_receipt(tx_hash)["contractAddress"]
152
153 # sanity check
154 assert w3.eth.get_code(address) == bytecode, (w3.eth.get_code(address), bytecode)
155
156 def factory(address):
157 return w3.eth.contract(
158 address, abi=abi, bytecode=bytecode, ContractFactoryClass=VyperContract
159 )
160
161 return w3.eth.contract(address, bytecode=deploy_bytecode), factory
162
163
164@pytest.fixture(scope="module")
165def deploy_blueprint_for(w3, no_optimize):
166 def deploy_blueprint_for(source_code, *args, **kwargs):
167 return _deploy_blueprint_for(w3, source_code, no_optimize, *args, **kwargs)
168
169 return deploy_blueprint_for
170
171
172@pytest.fixture(scope="module")
173def get_contract(w3, no_optimize):
174 def get_contract(source_code, *args, **kwargs):
175 return _get_contract(w3, source_code, no_optimize, *args, **kwargs)
176
177 return get_contract
178
179
180@pytest.fixture
181def get_logs(w3):
182 def get_logs(tx_hash, c, event_name):
183 tx_receipt = w3.eth.get_transaction_receipt(tx_hash)
184 return c._classic_contract.events[event_name]().processReceipt(tx_receipt)
185
186 return get_logs
187
188
189@pytest.fixture(scope="module")
190def assert_tx_failed(tester):
191 def assert_tx_failed(function_to_test, exception=TransactionFailed, exc_text=None):
192 snapshot_id = tester.take_snapshot()
193 with pytest.raises(exception) as excinfo:
194 function_to_test()
195 tester.revert_to_snapshot(snapshot_id)
196 if exc_text:
197 # TODO test equality
198 assert exc_text in str(excinfo.value), (exc_text, excinfo.value)
199
200 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