Tools for testing Ethereum applications

Read more in the documentation below. View the change log.

python -m pip install eth-tester

>>> from eth_tester import EthereumTester
>>> t = EthereumTester()
>>> t.get_accounts()
('0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf',
 '0x2B5AD5c4795c026514f8317c7a215E218DcCD6cF',
 '0x6813Eb9362372EEF6200f3b1dbC3f819671cBA69',
 '0x1efF47bc3a10a45D4B230B5d10E37751FE6AA718',
 '0xe1AB8145F7E55DC933d51a18c793F901A3A0b276',
 '0xE57bFE9F44b819898F47BF37E5AF72a0783e1141',
 '0xd41c057fd1c78805AAC12B0A94a405c0461A6FBb',
 '0xF1F6619B38A98d6De0800F1DefC0a6399eB6d30C',
 '0xF7Edc8FA1eCc32967F827C9043FcAe6ba73afA5c',
 '0x4CCeBa2d7D2B4fdcE4304d3e09a1fea9fbEb1528')

>>> t.get_balance('0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf')
1000000000000000000000000

>>> t.send_transaction({
...     'from': '0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf',
...     'to': '0x2B5AD5c4795c026514f8317c7a215E218DcCD6cF',
...     'gas': 30000,
...     'value': 1,
...     'max_fee_per_gas': 1000000000,
...     'max_priority_fee_per_gas': 1000000000,
...     'chain_id': 131277322940537,
...     'access_list': (
...         {
...             'address': '0xde0b295669a9fd93d5f28d9ec85e40f4cb697bae',
...             'storage_keys': (
...                 '0x0000000000000000000000000000000000000000000000000000000000000003',
...                 '0x0000000000000000000000000000000000000000000000000000000000000007',
...             )
...         },
...         {
...             'address': '0xbb9bc244d798123fde783fcc1c72d3bb8c189413',
...             'storage_keys': ()
...         },
...     )
... })
'0xc20b90af87bc65c3d748cf0a1fa54f3a86ffc94348e0fd91a70f1c5ba6ef4109'

>>> t.get_transaction_by_hash('0xc20b90af87bc65c3d748cf0a1fa54f3a86ffc94348e0fd91a70f1c5ba6ef4109')
{'type': '0x2',
 'hash': '0xc20b90af87bc65c3d748cf0a1fa54f3a86ffc94348e0fd91a70f1c5ba6ef4109',
 'nonce': 0,
 'block_hash': '0x28b95514984b0abbd91d88f1a542eaeeb810c24e0234e09891b7d6b3f94f47ed',
 'block_number': 1,
 'transaction_index': 0,
 'from': '0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf',
 'to': '0x2B5AD5c4795c026514f8317c7a215E218DcCD6cF',
 'value': 1,
 'gas': 30000,
 'data': '0x',
 'r': 60071646517429056848243893841817235885102606421189844318110381014348740252962,
 's': 55731679314783756278323646144996847004593793888590884914350251538533006990589,
 'v': 0,
 'chain_id': 131277322940537,
 'max_fee_per_gas': 1000000000,
 'max_priority_fee_per_gas': 1000000000,
 'access_list': ({'address': '0xde0B295669a9FD93d5F28D9Ec85E40f4cb697BAe',
   'storage_keys': ('0x0000000000000000000000000000000000000000000000000000000000000003',
    '0x0000000000000000000000000000000000000000000000000000000000000007')},
  {'address': '0xBB9bc244D798123fDe783fCc1C72d3Bb8C189413',
   'storage_keys': ()}),
 'gas_price': 1000000000}


>>> t.get_transaction_receipt('0xc20b90af87bc65c3d748cf0a1fa54f3a86ffc94348e0fd91a70f1c5ba6ef4109')
{'transaction_hash': '0xc20b90af87bc65c3d748cf0a1fa54f3a86ffc94348e0fd91a70f1c5ba6ef4109',
 'transaction_index': 0,
 'block_number': 1,
 'block_hash': '0x28b95514984b0abbd91d88f1a542eaeeb810c24e0234e09891b7d6b3f94f47ed',
 'cumulative_gas_used': 29600,
 'gas_used': 29600,
 'effective_gas_price': 1000000000,
 'contract_address': None,
 'logs': (),
 'type': '0x2',
 'status': 1}

The ethereum tester library strictly enforces the following input formats and types.

• Hexadecimal values must be text (not byte) strings. The 0x prefix is optional.
• Any address which contains mixed-case alpha characters will be validated as a checksummed address as specified by EIP-55
• 32-byte hashes must be hexadecimal encoded.
• Numeric values must be in their integer representation.

Similarly, ethereum tester ensures that return values conform to similar rules.

• 32-byte hashes will be returned in their hexadecimal encoded representation.
• Addresses will be returned in their hexadecimal representation and EIP55 checksummed.
• Numeric values will be returned as integers.

Any block_number parameter will accept the following string values.

• 'latest': for the latest mined block.
• 'pending': for the current un-mined block.
• 'earliest': for the genesis block.
• 'safe': for the last block that has passed 2/3 of attestations post-merge.
• 'finalized': for the last finalized block post-merge.

Note: These must be text strings (not byte stringS)

• eth_tester.EthereumTester(backend=None, validator=None, normalizer=None, auto_mine_transactions=True, fork_blocks=None)

The EthereumTester object is the sole API entrypoint. Instantiation of this object accepts the following parameters.

• backend: The chain backend being used. See the chain backends
• validator: The validator being used. See the validators
• normalizer: The normalizer being used. See the normalizers
• auto_mine_transactions: If truthy transactions will be automatically mined at the time they are submitted. See enable_auto_mine_transactions and disable_auto_mine_transactions.
• fork_blocks: configures which block numbers the various network hard fork rules will be activated. See fork-rules

>>> from eth_tester import EthereumTester
>>> t = EthereumTester()
>>> t
<eth_tester.main.EthereumTester at 0x102255710>

Ethereum tester uses the Paris (PoS) fork rules, starting at block 0.

The chain can only time travel forward in time.

The timestamp must be an integer, strictly greater than the current timestamp of the latest block.

Note: Time traveling will result in a new block being mined.

Manually mining blocks can be done with the following API. The coinbase parameter of these methods must be a hexadecimal encoded address.

Mines num_blocks new blocks, returning an iterable of the newly mined block hashes.

Mines a single new block, returning the mined block's hash.

By default, all transactions are mined immediately. This means that each transaction you send will result in a new block being mined, and that all blocks will only ever have at most a single transaction. This behavior can be controlled with the following methods.

Turns on auto-mining of transactions.

Turns off auto-mining of transactions.

The following API can be used to interact with account data. The account parameter in these methods must be a hexadecimal encode address.

EthereumTester.get_accounts()

Returns an iterable of the accounts that the tester knows about. All accounts in this list will be EIP55 checksummed.

>>> t.get_accounts()
('0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1',
 '0x7d577a597B2742b498Cb5Cf0C26cDCD726d39E6e',
 ...
 '0x90F0B1EBbbA1C1936aFF7AAf20a7878FF9e04B6c')

Adds a new account for the given private key. Returns the hex encoded address of the added account.

>>> t.add_account('0x58d23b55bc9cdce1f18c2500f40ff4ab7245df9a89505e9b1fa4851f623d241d')
'0xdc544d1aa88ff8bbd2f2aec754b1f1e99e1812fd'

By default, added accounts are unlocked and do not have a password. If you would like to add an account which has a password, you can supply the password as the second parameter.

>>> t.add_account('0x58d23b55bc9cdce1f18c2500f40ff4ab7245df9a89505e9b1fa4851f623d241d', 'my-secret')
'0xdc544d1aa88ff8bbd2f2aec754b1f1e99e1812fd'

Unlocks the given account if the provided password matches.

Raises a ValidationError if:

• The account is not known.
• The password does not match.
• The account was created without a password.

>>> t.unlock_account('0xdc544d1aa88ff8bbd2f2aec754b1f1e99e1812fd', 'my-secret')

By default, accounts will be unlocked indefinitely. You can however unlock an account for a specified amount of time by providing the desired duration in seconds.

# unlock for 1 hour.
>>> t.unlock_account('0xdc544d1aa88ff8bbd2f2aec754b1f1e99e1812fd', 'my-secret', 60 * 60)

Locks the provided account.

Raises a ValidationError if:

• The account is not known
• The account does not have a password.

Returns the balance, in wei, for the provided account.

>>> t.get_balance('0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1')
1000004999999999999999999

Returns the nonce for the provided account.

>>> t.get_nonce('0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1')
1

Returns the code for the given account.

>>> t.get_code('0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1')
"0x"

Returns the transaction for the given hash, raising a TransactionNotFound exception if the transaction cannot be found.

>>> t.get_transaction_by_hash('0x21ae665f707e12a5f1bb13ef8c706b65cc5accfd03e7067ce683d831f51122e6')
{'type': '0x2',
 'hash': '0x21ae665f707e12a5f1bb13ef8c706b65cc5accfd03e7067ce683d831f51122e6',
 'nonce': 0,
 'block_hash': '0x810731efeb7498fc0ac3bc7c72a71571b672c9fdbfbfd8b435f483e368e8ef7e',
 'block_number': 1,
 'transaction_index': 0,
 'from': '0x2B5AD5c4795c026514f8317c7a215E218DcCD6cF',
 'to': '0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf',
 'value': 1337,
 'gas': 21000,
 'data': '0x',
 'r': 1713666669454033023988006960017431058214051587080823768269189498559514600280,
 's': 32003859822305799628524852194521134173285969678963273753063458725692016415033,
 'v': 0,
 'chain_id': 131277322940537,
 'max_fee_per_gas': 2000000000,
 'max_priority_fee_per_gas': 500000000,
 'access_list': (),
 'gas_price': 1375000000}

Note: For unmined transaction, transaction_index, block_number and block_hash will all be None.

Returns the block for the given block_number. See block numbers for named block numbers you can use. If full_transactions is truthy, then the transactions array will be populated with full transaction objects as opposed to their hashes.

Raises BlockNotFound if a block for the given number cannot be found.

>>> t.get_block_by_number(1)
{'number': 1,
 'hash': '0xd481955268d1f3db58ee61685a899a35e33e8fd35b9cc0812f85b9f06757140e',
 'parent_hash': '0x5be984ab842071903ee443a5dee92603bef42de35b4e10928e753f7e88a7163a',
 'nonce': '0x0000000000000000',
 'sha3_uncles': '0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347',
 'logs_bloom': 0,
 'transactions_root': '0xef1e11d99f7db22fd93c6a10d44753d4a93e9f6ecb2f1e5030a0a91f1d3b07ac',
 'receipts_root': '0x611e48488cf80b4c31f01ad45b6ebea533a68255a6d0240d434d9366a3582010',
 'state_root': '0x9ce568dcaa6f130d733b333304f2c26a19334ed328a7eb9bb31707306381ba65',
 'coinbase': '0x0000000000000000000000000000000000000000',
 'difficulty': 0,
 'total_difficulty': 0,
 'mix_hash': '0x0000000000000000000000000000000000000000000000000000000000000000',
 'size': 751,
 'extra_data': '0x0000000000000000000000000000000000000000000000000000000000000000',
 'gas_limit': 3141592,
 'gas_used': 29600,
 'timestamp': 1633669276,
 'transactions': ('0xc20b90af87bc65c3d748cf0a1fa54f3a86ffc94348e0fd91a70f1c5ba6ef4109',),
 'uncles': (),
 'base_fee_per_gas': 875000000}

Returns the block for the given block_hash. The full_transactions parameter behaves the same as in get_block_by_number.

Raises BlockNotFound if a block for the given hash cannot be found.

>>> t.get_block_by_hash('0x0f50c8ea0f67ce0b7bff51ae866159edc443bde87de2ab26010a15b777244ddd')
{'number': 1,
 'hash': '0xd481955268d1f3db58ee61685a899a35e33e8fd35b9cc0812f85b9f06757140e',
 'parent_hash': '0x5be984ab842071903ee443a5dee92603bef42de35b4e10928e753f7e88a7163a',
 'nonce': '0x0000000000000000',
 'sha3_uncles': '0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347',
 'logs_bloom': 0,
 'transactions_root': '0xef1e11d99f7db22fd93c6a10d44753d4a93e9f6ecb2f1e5030a0a91f1d3b07ac',
 'receipts_root': '0x611e48488cf80b4c31f01ad45b6ebea533a68255a6d0240d434d9366a3582010',
 'state_root': '0x9ce568dcaa6f130d733b333304f2c26a19334ed328a7eb9bb31707306381ba65',
 'coinbase': '0x0000000000000000000000000000000000000000',
 'difficulty': 0,
 'total_difficulty': 0,
 'mix_hash': '0x0000000000000000000000000000000000000000000000000000000000000000',
 'size': 751,
 'extra_data': '0x0000000000000000000000000000000000000000000000000000000000000000',
 'gas_limit': 3141592,
 'gas_used': 29600,
 'timestamp': 1633669276,
 'transactions': ('0xc20b90af87bc65c3d748cf0a1fa54f3a86ffc94348e0fd91a70f1c5ba6ef4109',),
 'uncles': (),
 'base_fee_per_gas': 875000000}

Returns the receipt for the given transaction_hash, raising TransactionNotFound if no transaction can be found for the given hash.

>>> t.get_transaction_receipt('0x9a7cc8b7accf54ecb1901bf4d0178f28ca457bb9f9c245692c0ca8fabef08d3b')
 {'block_hash': '0x878f779d8bb25b25fb78fc16b8d64d70a5961310ef1689571aec632e9424290c',
 'block_number': 2,
 'contract_address': None,
 'cumulative_gas_used': 23154,
 'gas_used': 23154,
 'logs': ({'address': '0xd6F084Ee15E38c4f7e091f8DD0FE6Fe4a0E203Ef',
   'block_hash': '0x878f779d8bb25b25fb78fc16b8d64d70a5961310ef1689571aec632e9424290c',
   'block_number': 2,
   'data': '0x',
   'log_index': 0,
   'topics': (
    '0xf70fe689e290d8ce2b2a388ac28db36fbb0e16a6d89c6804c461f65a1b40bb15',
    '0x0000000000000000000000000000000000000000000000000000000000003039'),
   'transaction_hash': '0x9a7cc8b7accf54ecb1901bf4d0178f28ca457bb9f9c245692c0ca8fabef08d3b',
   'transaction_index': 0,
   'type': 'mined'},),
 'transaction_hash': '0x9a7cc8b7accf54ecb1901bf4d0178f28ca457bb9f9c245692c0ca8fabef08d3b',
 'transaction_index': 0}

• Receipts for unmined transactions will have all of block_hash, block_number and transaction_index set to None.
• Receipts for transactions which create a contract will have the created contract address in the contract_address field.

A transaction is a formatted as a dictionary with the following keys and values.

• from: The address of the account sending the transaction (hexadecimal string).
• to: The address of the account the transaction is being sent to. Empty string should be used to trigger contract creation (hexadecimal string).
• gas: Sets the gas limit for transaction execution (integer).
• value: The amount of ether in wei that should be sent with the transaction (integer).
• data: The data for the transaction (hexadecimal string).
• chain_id: The integer id for the chain the transaction is meant to interact with.

In addition to the above, the following parameters are added based on the type of transaction being sent:

• gas_price: Sets the price per unit of gas in wei that will be paid for transaction execution (integer).

• gas_price: Sets the price per unit of gas in wei that will be paid for transaction execution (integer).
• access_list (optional): Specifies accounts and storage slots expected to be accessed, based on the transaction, in order to gain a discount on the gas for those executions (see quickstart example for usage).

• max_fee_per_gas: Sets the maximum fee per unit of gas in wei that will be paid for transaction execution (integer).
• max_priority_fee_per_gas: Sets the fee per unit of gas in wei that is sent to the coinbase address as an incentive for including the transaction (integer).
• access_list (optional): Specifies accounts and storage slots expected to be accessed, based on the transaction, in order to gain a discount on the gas for those executions (see quickstart example for usage).

Sends the provided transaction object, returning the transaction_hash for the sent transaction.

Executes the provided transaction object at the evm state from the block denoted by the block_number parameter, returning the resulting bytes return value from the evm.

Executes the provided transaction object, measuring and returning the gas consumption.

Return the historical gas information for the number of blocks specified as the block_count starting from newest_block. Note that specifying reward_percentiles has no effect on the response and so reward will always return an empty list.

Creates a new filter for newly mined blocks. Returns the filter_id which can be used to retrieve the block hashes for the mined blocks.

>>> filter_id = t.create_block_filter()
>>> filter_id = t.create_block_filter()
>>> t.mine_blocks(3)
>>> t.get_only_filter_changes(filter_id)
('0x07004287f82c1a7ab15d7b8baa03ac14d7e9167ab74e47e1dc4bd2213dd18431',
 '0x5e3222c506585e1202da08c7231afdc5e472c777c245b822f44f141d335c744a',
 '0x4051c3ba3dcca95da5db1be38e44f5b47fd1a855ba522123e3254fe3f8e271ea')
>>> t.mine_blocks(2)
>>> t.get_only_filter_changes(filter_id)
('0x6649c3a7cb3c7ede3a4fd10ae9dd63775eccdafe39ace5f5a9ae81d360089fba',
 '0x04890a08bca0ed2f1496eb29c5dc7aa66014c85377c6d9d9c2c315f85204b39c')
>>> t.get_all_filter_logs(filter_id)
('0x07004287f82c1a7ab15d7b8baa03ac14d7e9167ab74e47e1dc4bd2213dd18431',
 '0x5e3222c506585e1202da08c7231afdc5e472c777c245b822f44f141d335c744a',
 '0x4051c3ba3dcca95da5db1be38e44f5b47fd1a855ba522123e3254fe3f8e271ea',
 '0x6649c3a7cb3c7ede3a4fd10ae9dd63775eccdafe39ace5f5a9ae81d360089fba',
 '0x04890a08bca0ed2f1496eb29c5dc7aa66014c85377c6d9d9c2c315f85204b39c')

Creates a new filter for pending transactions. Returns the filter_id which can be used to retrieve the transaction hashes for the pending transactions.

>>> filter_id = t.create_pending_transaction_filter()
>>> t.send_transaction({...})
'0x07f20bf9586e373ac914a40e99119c4932bee343d89ba852ccfc9af1fd541566'
>>> t.send_transaction({...})
'0xff85f7751d132b66c03e548e736f870797b0f24f3ed41dfe5fc628eb2cbc3505'
>>> t.get_only_filter_changes(filter_id)
('0x07f20bf9586e373ac914a40e99119c4932bee343d89ba852ccfc9af1fd541566',
 '0xff85f7751d132b66c03e548e736f870797b0f24f3ed41dfe5fc628eb2cbc3505')
>>> t.send_transaction({...})
'0xb07801f7e8b1cfa52b64271fa2673c4b8d64cc21cdbc5fde51d5858c94c2d26a'
>>> t.get_only_filter_changes(filter_id)
('0xb07801f7e8b1cfa52b64271fa2673c4b8d64cc21cdbc5fde51d5858c94c2d26a',)
>>> t.get_all_filter_logs(filter_id)
('0x07f20bf9586e373ac914a40e99119c4932bee343d89ba852ccfc9af1fd541566',
 '0xff85f7751d132b66c03e548e736f870797b0f24f3ed41dfe5fc628eb2cbc3505',
 '0xb07801f7e8b1cfa52b64271fa2673c4b8d64cc21cdbc5fde51d5858c94c2d26a')

Creates a new filter for logs produced by transactions. The parameters for this function can be used to filter the log entries.

>>> filter_id = t.create_log_filter()
>>> t.send_transaction({...})  # something that produces a log entry
'0x728bf75fc7d23845f328d2223df7fe9cafc6e7d23792457b625d5b60d2b22b7c'
>>> t.send_transaction({...})  # something that produces a log entry
'0x63f5b381ffd09940ce22c45a3f4e163bd743851cb6b4f43771fbf0b3c14b2f8a'
>>> t.get_only_filter_changes(filter_id)
({'address': '0xd6F084Ee15E38c4f7e091f8DD0FE6Fe4a0E203Ef',
  'block_hash': '0x68c0f318388003b652eae334efbed8bd345c469bd0ca77469183fc9693c23e13',
  'block_number': 11,
  'data': '0x',
  'log_index': 0,
  'topics': ('0xf70fe689e290d8ce2b2a388ac28db36fbb0e16a6d89c6804c461f65a1b40bb15',
   '0x0000000000000000000000000000000000000000000000000000000000003039'),
  'transaction_hash': '0x728bf75fc7d23845f328d2223df7fe9cafc6e7d23792457b625d5b60d2b22b7c',
  'transaction_index': 0,
  'type': 'mined'},
 {'address': '0xd6F084Ee15E38c4f7e091f8DD0FE6Fe4a0E203Ef',
  'block_hash': '0x07d7e46be6f9ba53ecd4323fb99ec656e652c4b14f4b8e8a244ee7f997464725',
  'block_number': 12,
  'data': '0x',
  'log_index': 0,
  'topics': ('0xf70fe689e290d8ce2b2a388ac28db36fbb0e16a6d89c6804c461f65a1b40bb15',
   '0x0000000000000000000000000000000000000000000000000000000000010932'),
  'transaction_hash': '0x63f5b381ffd09940ce22c45a3f4e163bd743851cb6b4f43771fbf0b3c14b2f8a',
  'transaction_index': 0,
  'type': 'mined'})

Removes the filter for the provided filter_id. If no filter is found for the given filter_id, raises FilterNotFound.

Returns all new values for the provided filter_id that have not previously been returned through this API. Raises FilterNotFound if no filter is found for the given filter_id.

Returns all values for the provided filter_id. Raises FilterNotFound if no filter is found for the given filter_id.

Takes a snapshot of the current chain state and returns the snapshot id.

Reverts the chain to the chain state associated with the given snapshot_id. Raises SnapshotNotFound if no snapshot is known for the given id.

Raised in cases where a transaction cannot be found for the provided transaction hash.

Raised in cases where a block cannot be found for either a provided number or hash.

Raised in cases where a filter cannot be found for the provided filter id.

Raised in cases where a snapshot cannot be found for the provided snapshot id.

Ethereum tester is written using a pluggable backend system.

Ethereum tester does not install any of the dependencies needed to use the various backends by default. You can however install ethereum tester with the necessary dependencies using the following method.

$ python -m pip install eth-tester[<backend-name>]

You should replace <backend-name> with the name of the desired testing backend. Available backends are:

• py-evm: PyEVM (alpha) (experimental)

You can select which backend in a few different ways.

The most direct way is to manually pass in the backend instance you wish to use.

>>> from eth_tester import EthereumTester, MockBackend
>>> t = EthereumTester(backend=MockBackend())

Ethereum tester also supports configuration using the environment variable ETHEREUM_TESTER_CHAIN_BACKEND. This should be set to the import path for the backend class you wish to use.

Ethereum tester can be used with the following backends.

• MockBackend
• PyEVM (experimental)

This backend has limited functionality. It cannot perform any VM computations. It mocks out all of the objects and interactions.

>>> from eth_tester import EthereumTester, MockBackend
>>> t = EthereumTester(MockBackend())

WARNING Py-EVM is experimental and should not be relied on for mission critical testing at this stage.

Uses the experimental Py-EVM library.

>>> from eth_tester import EthereumTester, PyEVMBackend
>>> t = EthereumTester(PyEVMBackend())

If you need to specify custom genesis parameters and state, you can build your own parameters dict to use instead of the default when initializing a backend. Only default values can be overridden or a ValueError will be raised.

# Default Genesis Parameters

default_genesis_params = {
    "coinbase": GENESIS_COINBASE,
    "difficulty": GENESIS_DIFFICULTY,
    "extra_data": GENESIS_EXTRA_DATA,
    "gas_limit": GENESIS_GAS_LIMIT,
    "mix_hash": GENESIS_MIX_HASH,
    "nonce": GENESIS_NONCE,
    "receipt_root": BLANK_ROOT_HASH,
    "timestamp": int(time.time()),
    "transaction_root": BLANK_ROOT_HASH,
}

To generate a genesis parameters dict with an overridden parameters, pass a genesis_overrides dict
to PyEVM.generate_genesis_params.

>>> from eth_tester import PyEVMBackend, EthereumTester

>>> genesis_overrides = {'gas_limit': 4500000}
>>> custom_genesis_params = PyEVMBackend.generate_genesis_params(overrides=genesis_overrides)

# Generates the following `dict`:

# custom_genesis_params = {
#     "coinbase": GENESIS_COINBASE,
#     "difficulty": GENESIS_DIFFICULTY,
#     "extra_data": GENESIS_EXTRA_DATA,
#     "gas_limit": 4500000    # <<< Overridden Value <<<
#     "mix_hash": GENESIS_MIX_HASH,
#     "nonce": GENESIS_NONCE,
#     "receipt_root": BLANK_ROOT_HASH,
#     "timestamp": int(time.time()),
#     "transaction_root": BLANK_ROOT_HASH,
# }

Then pass the generated custom_genesis_params dict to the backend's __init__

>>> from eth_tester import PyEVMBackend, EthereumTester
>>> pyevm_backend = PyEVMBackend(genesis_parameters=custom_genesis_params)
>>> t = EthereumTester(backend=pyevm_backend)

Similarly to genesis_parameters, override the genesis state by passing in an overrides dict to PyEVMBackend.generate_genesis_state. Optionally, provide num_accounts to set the number of accounts.

For more control on which accounts the backend generates, use the from_mnemonic() classmethod. Give it a mnemonic (and optionally the number of accounts) and it will use that information to generate the accounts. Optionally, provide a genesis_state_overrides dict to adjust the genesis_state.

>>> from eth_tester import PyEVMBackend, EthereumTester
>>> from eth_utils import to_wei
>>> from hexbytes import HexBytes
>>>
>>> pyevm_backend = PyEVMBackend.from_mnemonic(
>>>    'test test test test test test test test test test test junk',
>>>    genesis_state_overrides={'balance': to_wei(1000000, 'ether')}
>>> )
>>> t = EthereumTester(backend=pyevm_backend)
>>> print(t.get_accounts()[0])  # Outputs 0x1e59ce931B4CFea3fe4B875411e280e173cB7A9C
>>> print(t.get_balance('0x1e59ce931B4CFea3fe4B875411e280e173cB7A9C'))  # Outputs 1000000000000000000000000

NOTE: The same state is applied to all generated test accounts.

# Default Account Genesis State

default_account_state = {
    'balance': to_wei(1000000, 'ether'),
    'storage': {},
    'code': b'',
    'nonce': 0,
}

For Example, to create 3 test accounts, each with a balance of 100 ETH each:

>>> from eth_tester import EthereumTester, PyEVMBackend
>>>  from eth_utils import to_wei

>>> state_overrides = {'balance': to_wei(100, 'ether')}
>>> custom_genesis_state = PyEVMBackend.generate_genesis_state(overrides=state_overrides, num_accounts=3)

# Then pass the generated `custom_genesis_state` `dict` to the backend's `__init__`

>>> pyevm_backend = PyEVMBackend(genesis_state=custom_genesis_state)
>>> t = EthereumTester(backend=pyevm_backend)

The base class eth_tester.backends.base.BaseChainBackend is the recommended base class to begin with if you wish to write your own backend.

Details on implementation are beyond the scope of this document.

Ethereum tester uses two formats for data.

• The normal format is the data format the is expected as input arguments to all EthereumTester methods as well as the return types from all method calls.
• The canonical format is the data format that is used internally by the backend class.

Ethereum tester enforces strict validation rules on these formats.

The canonical format is intended for low level handling by backends.

• 32 byte hashes: bytes of length 32
• Arbitrary length strings: bytes
• Addresses: bytes of length 20
• Integers: int
• Array Types: tuple

The normal format is intended for use by end users.

• 32 byte hashes: 0x prefixed hexadecimal encoded text strings (not byte strings)
• Arbitrary length strings: 0x prefixed hexadecimal encoded text strings (not byte strings)
• Addresses: 0x prefixed and EIP55 checksummed hexadecimal encoded text strings (not byte strings)
• Integers: int
• Array Types: tuple

Beware! Here there be dragons... This section of the documentation is only relevant if you intend to build tooling on top of this library.

The ethereum tester provides strong guarantees that backends can be swapped out seamlessly without effecting the data formats of both the input arguments and return values. This is accomplished using a two-step process of strict normalization and validation.

All inputs to the methods of the EthereumTester are first validated then normalized to a canonical format. Return values are put through this process as well, first validating the data returned by the backend, and then normalizing it from the canonical format to the normal form before being returned.

The EthereumTester delegates normalization to whatever normalizer was passed in during instantiation. If no value was provided, the default normalizer will be used from eth_tester.normalization.default.DefaultNormalizer.

The specifics of this object are beyond the scope of this document.

The EthereumTester delegates validation to whatever validator was passed in during instantiation. If no value was provided, the default validator will be used from eth_tester.validation.default.DefaultValidator.

The specifics of this object are beyond the scope of this document.

See the web3.py documentation for information on the EthereumTester provider which integrates with this library.

If you would like to hack on eth-tester, please check out the Snake Charmers Tactical Manual for information on how we do:

• Testing
• Pull Requests
• Documentation

We use pre-commit to maintain consistent code style. Once installed, it will run automatically with every commit. You can also run it manually with make lint. If you need to make a commit that skips the pre-commit checks, you can do so with git commit --no-verify.

You can set up your dev environment with:

git clone git@github.com:ethereum/eth-tester.git
cd eth-tester
virtualenv -p python3 venv
. venv/bin/activate
python -m pip install -e ".[dev]"
pre-commit install

To release a new version:

make release bump=$$VERSION_PART_TO_BUMP$$

The version format for this repo is {major}.{minor}.{patch} for stable, and {major}.{minor}.{patch}-{stage}.{devnum} for unstable (stage can be alpha or beta).

To issue the next version in line, specify which part to bump, like make release bump=minor or make release bump=devnum. This is typically done from the main branch, except when releasing a beta (in which case the beta is released from main, and the previous stable branch is released from said branch).

If you are in a beta version, make release bump=stage will switch to a stable.

To issue an unstable version when the current version is stable, specify the new version explicitly, like make release bump="--new-version 4.0.0-alpha.1 devnum"