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