Ethereum Tester

Tools for testing ethereum based applications.

Installation

pip install eth-tester

Quick Start

>>> from eth_tester import EthereumTester
>>> t = EthereumTester()
>>> t.get_accounts()
('0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1',
 '0x7d577a597B2742b498Cb5Cf0C26cDCD726d39E6e',
 '0xDCEceAF3fc5C0a63d195d69b1A90011B7B19650D',
 '0x598443F1880Ef585B21f1d7585Bd0577402861E5',
 '0x13cBB8D99C6C4e0f2728C7d72606e78A29C4E224',
 '0x77dB2BEBBA79Db42a978F896968f4afCE746ea1F',
 '0x24143873e0E0815fdCBcfFDbe09C979CbF9Ad013',
 '0x10A1c1CB95c92EC31D3f22C66Eef1d9f3F258c6B',
 '0xe0FC04FA2d34a66B779fd5CEe748268032a146c0',
 '0x90F0B1EBbbA1C1936aFF7AAf20a7878FF9e04B6c')
>>> t.get_balance('0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1')
1000000000000000000000000
>>> t.send_transaction({'from': '0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1', 'to': '0x7d577a597B2742b498Cb5Cf0C26cDCD726d39E6e', 'gas': 21000, 'value': 1})
'0x140c1da1370a908e4c0f7c6e33bb97182011707c6a9aff954bef1084c8a48b25'
>>> t.get_transaction_by_hash('0x140c1da1370a908e4c0f7c6e33bb97182011707c6a9aff954bef1084c8a48b25')
{'block_hash': '0x89c03ecb6bbf3ff533b04a663fa98d59c9d985de806d1a9dcafaad7c993ee6e8',
 'block_number': 0,
 'data': '0x',
 'from': '0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1',
 'gas': 21000,
 'gas_price': 1,
 'hash': '0x140c1da1370a908e4c0f7c6e33bb97182011707c6a9aff954bef1084c8a48b25',
 'nonce': 0,
 'r': 114833774457827084417823702749930473879683934597320921824765632039428214735160,
 's': 52192522150044217242428968890330558187037131043598164958282684822175843828481,
 'to': '0x7d577a597B2742b498Cb5Cf0C26cDCD726d39E6e',
 'transaction_index': 0,
 'v': 27,
 'value': 1}

>>> t.get_transaction_receipt('0x140c1da1370a908e4c0f7c6e33bb97182011707c6a9aff954bef1084c8a48b25')
{'block_hash': '0x89c03ecb6bbf3ff533b04a663fa98d59c9d985de806d1a9dcafaad7c993ee6e8',
 'block_number': 0,
 'contract_address': None,
 'cumulative_gas_used': 21000,
 'gas_used': 21000,
 'logs': (),
 'transaction_hash': '0x140c1da1370a908e4c0f7c6e33bb97182011707c6a9aff954bef1084c8a48b25',
 'transaction_index': 0}

Development

pip install -e ".[dev]"

Running the tests

You can run the tests with:

py.test tests

Or you can install tox to run the full test suite.

Releasing

Pandoc is required for transforming the markdown README to the proper format to render correctly on pypi.

For Debian-like systems:

apt install pandoc

Or on OSX:

brew install pandoc

To release a new version:

bumpversion $$VERSION_PART_TO_BUMP$$
git push && git push --tags
make release

How to bumpversion

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, use bumpversion and specify which part to bump, like bumpversion minor or bumpversion devnum.

If you are in a beta version, bumpversion stage will switch to a stable.

To issue an unstable version when the current version is stable, specify the new version explicitly, like bumpversion --new-version 4.0.0-alpha.1 devnum

Documentation

Input and output data formats

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

• Hexidecimal 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 hexidecimal 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 hexidecimal encoded representation.
• Addresses will be returned in their hexidecimal representation and EIP55 checksummed.
• Numeric values will be returned as integers.

Block Numbers

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.

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

eth_tester.EthereumTester

API

Instantiation

• 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 to used. See the validators
• normalizer: The normalizer to 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>

Fork Rules

Ethereum tester uses the Byzantium rules, starting at block 0.

Time Travel

The chain can only time travel forward in time.

EthereumTester.time_travel(timestamp)

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.

Mining

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

EthereumTester.mine_blocks(num_blocks=1, coinbase=None)

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

EthereumTester.mine_block(coinbase=None)

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

Auto-mining transactions

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.

EthereumTester.enable_auto_mine_transactions()

Turns on auto-mining of transactions.

EthereumTester.disable_auto_mine_transactions()

Turns off auto-mining of transactions.

Accounts

The following API can be used to interact with account data. The account parameter in these methods must be a hexidecimal 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')

EthereumTester.add_account(private_key, password=None)

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'

EthereumTester.unlock_account(account, password, unlock_seconds=None)

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)

EthereumTester.lock_account(account)

Locks the provide account.

Raises a ValidationError if:

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

EthereumTester.get_balance(account) -> integer

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

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

EthereumTester.get_nonce(account) -> integer

Returns the nonce for the provided account.

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

EthereumTester.get_code(account) -> hex string

Returns the code for the given account.

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

Blocks, Transactions, and Receipts

EthereumTester.get_transaction_by_hash(transaction_hash) -> transaction-object

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

>>> t.get_transaction_by_hash('0x140c1da1370a908e4c0f7c6e33bb97182011707c6a9aff954bef1084c8a48b25')
{'block_hash': '0x89c03ecb6bbf3ff533b04a663fa98d59c9d985de806d1a9dcafaad7c993ee6e8',
 'block_number': 0,
 'hash': '0x140c1da1370a908e4c0f7c6e33bb97182011707c6a9aff954bef1084c8a48b25',
 'transaction_index': 0,
 'from': '0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1',
 'to': '0x7d577a597B2742b498Cb5Cf0C26cDCD726d39E6e',
 'value': 1,
 'gas': 21000,
 'gas_price': 1,
 'nonce': 0,
 'data': '0x',
 'v': 27,
 'r': 114833774457827084417823702749930473879683934597320921824765632039428214735160,
 's': 52192522150044217242428968890330558187037131043598164958282684822175843828481}

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

EthereumTester.get_block_by_number(block_number, full_transactions=False) -> block-object

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)
{'difficulty': 131072,
 'extra_data': '0x0000000000000000000000000000000000000000000000000000000000000000',
 'gas_limit': 999023468,
 'gas_used': 0,
 'hash': '0x0f50c8ea0f67ce0b7bff51ae866159edc443bde87de2ab26010a15b777244ddd',
 'logs_bloom': 0,
 'miner': '0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1',
 'nonce': '0x0000000000000000',
 'number': 1,
 'parent_hash': '0x89c03ecb6bbf3ff533b04a663fa98d59c9d985de806d1a9dcafaad7c993ee6e8',
 'sha3_uncles': '0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347',
 'size': 472,
 'state_root': '0xbd92123803c9e71018617ce3dc6cbbdf130973bdbd0e14ff340c57c8a835b74b',
 'timestamp': 1410973360,
 'total_difficulty': 262144,
 'transactions': (),
 'transactions_root': '0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421',
 'uncles': ()}

EthereumTester.get_block_by_hash(block_hash, full_transactions=True) -> block-object

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')
{'difficulty': 131072,
 'extra_data': '0x0000000000000000000000000000000000000000000000000000000000000000',
 'gas_limit': 999023468,
 'gas_used': 0,
 'hash': '0x0f50c8ea0f67ce0b7bff51ae866159edc443bde87de2ab26010a15b777244ddd',
 'logs_bloom': 0,
 'miner': '0x82A978B3f5962A5b0957d9ee9eEf472EE55B42F1',
 'nonce': '0x0000000000000000',
 'number': 1,
 'parent_hash': '0x89c03ecb6bbf3ff533b04a663fa98d59c9d985de806d1a9dcafaad7c993ee6e8',
 'sha3_uncles': '0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347',
 'size': 472,
 'state_root': '0xbd92123803c9e71018617ce3dc6cbbdf130973bdbd0e14ff340c57c8a835b74b',
 'timestamp': 1410973360,
 'total_difficulty': 262144,
 'transactions': (),
 'transactions_root': '0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421',
 'uncles': ()}

EthereumTester.get_transaction_receipt(transaction_hash)

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.

Transaction Sending

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

• from: The address of the account sending the transaction (hexidecimal string).
• to: The address of the account the transaction is being sent to. Empty string should be used to trigger contract creation (hexidecimal string).
• gas: Sets the gas limit for transaction execution (integer).
• gas_price: Sets the price per unit of gas in wei that will be paid 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 (hexidecimal string).

Methods

EthereumTester.send_transaction(transaction) -> transaction_hash

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

EthereumTester.call(transaction, block_number='latest')

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.

EthereumTester.estimate_gas(transaction)

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

Logs and Filters

EthereumTester.create_block_filter() -> integer

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')

EthereumTester.create_pending_transaction_filter() -> integer

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')

EthereumTester.create_log_filter(from_block=None, to_block=None, address=None, topics=None) -> integer

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'})

See the filtering guide for detailed information on how to use filters.

EthereumTester.delete_filter(filter_id)

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

EthereumTester.get_only_filter_changes(filter_id) -> transaction_hash or block_hash or log_entry

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.

EthereumTester.get_all_filter_logs(filter_id) -> transaction_hash or block_hash or log_entry

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

Snapshots and Resetting

EthereumTester.take_snapshot() -> snapshot_id

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

EthereumTester.revert_to_snapshot(snapshot_id)

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

Errors and Exceptions

eth_tester.exceptions.TransactionNotFound

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

eth_tester.exceptions.BlockNotFound

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

eth_tester.exceptions.FilterNotFound

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

eth_tester.exceptions.SnapshotNotFound

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

Backends

Ethereum tester is written using a pluggable backend system.

Backend Dependencies

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.

$ 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)

Selecting a Backend

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.

Available Backends

Ethereum tester can be used with the following backends.

• PyEVM (experimental)
• MockBackend

MockBackend

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())

PyEVM (experimental)

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())

PyEVM Genesis Parameters and State

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 = {
    "bloom": 0,
    "coinbase": GENESIS_COINBASE,
    "difficulty": GENESIS_DIFFICULTY,
    "extra_data": GENESIS_EXTRA_DATA,
    "gas_limit": GENESIS_GAS_LIMIT,
    "gas_used": 0,
    "mix_hash": GENESIS_MIX_HASH,
    "nonce": GENESIS_NONCE,
    "block_number": GENESIS_BLOCK_NUMBER,
    "parent_hash": GENESIS_PARENT_HASH,
    "receipt_root": BLANK_ROOT_HASH,
    "timestamp": int(time.time()),
    "transaction_root": BLANK_ROOT_HASH,
    "uncles_hash": EMPTY_RLP_LIST_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 = {
#     "bloom": 0,
#     "coinbase": GENESIS_COINBASE,
#     "difficulty": GENESIS_DIFFICULTY,
#     "extra_data": GENESIS_EXTRA_DATA,
#     "gas_limit": 4500000    # <<< Overidden Value <<<
#     "gas_used": 0,
#     "mix_hash": GENESIS_MIX_HASH,
#     "nonce": GENESIS_NONCE,
#     "block_number": GENESIS_BLOCK_NUMBER,
#     "parent_hash": GENESIS_PARENT_HASH,
#     "receipt_root": BLANK_ROOT_HASH,
#     "timestamp": int(time.time()),
#     "transaction_root": BLANK_ROOT_HASH,
#     "uncles_hash": EMPTY_RLP_LIST_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)

Overriding genesis state is similar to overriding genesis state, but requires the consideration of test accounts. To override the genesis state of accounts, pass a state_overrides dict to PyEVM.generate_genesis_state, and optionally, the number of accounts to create.

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)

Implementing Custom Backends

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.

Data Formats

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.

Canonical 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

Normal Formats

The normal format is intended for use by end users.

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

Normalization and Validation

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.

Normalization

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 beyong the scope of this document.

Validation

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 beyong the scope of this document.

Use with Web3.py

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