VM Tests¶

The VM tests aim is to test the basic workings of the VM in isolation.

Location	/VMTests
Supported Hardforks	Currently only Homestead
Status	Actively supported

This is specifically not meant to cover transaction, creation or call processing, or management of the state trie. Indeed at least one implementation tests the VM without calling into any Trie code at all.

A VM test is based around the notion of executing a single piece of code as part of a transaction, described by the exec portion of the test. The overarching environment in which it is executed is described by the env portion of the test and includes attributes of the current and previous blocks. A set of pre-existing accounts are detailed in the pre portion and form the world state prior to execution. Similarly, a set of accounts are detailed in the post portion to specify the end world state.

The gas remaining (gas), the log entries (logs) as well as any output returned from the code (out) is also detailed.

Test Implementation¶

It is generally expected that the test implementer will read env, exec and pre then check their results against gas, logs, out, post and callcreates. If an exception is expected, then latter sections are absent in the test. Since the reverting of the state is not part of the VM tests.

Because the data of the blockchain is not given, the opcode BLOCKHASH could not return the hashes of the corresponding blocks. Therefore we define the hash of block number n to be SHA3-256(“n”).

Since these tests are meant only as a basic test of VM operation, the CALL and CREATE instructions are not actually executed. To provide the possibility of testing to guarantee they were actually run at all, a separate portion callcreates details each CALL or CREATE operation in the order they would have been executed. Furthermore, gas required is simply that of the VM execution: the gas cost for transaction processing is excluded.

Test Structure¶

{
   "test name 1": {
           "env": { ... },
           "pre": { ... },
           "exec": { ... },
           "gas": { ... },
           "logs": { ... },
           "out": { ... },
           "post": { ... },
           "callcreates": { ... }
   },
   "test name 2": {
           "env": { ... },
           "pre": { ... },
           "exec": { ... },
           "gas": { ... },
           "logs": { ... },
           "out": { ... },
           "post": { ... },
           "callcreates": { ... }
   },
   ...
}

The env Section¶

currentCoinbase: The current block’s coinbase address, to be returned by the COINBASE instruction.
currentDifficulty: The current block’s difficulty, to be returned by the DIFFICULTY instruction.
currentGasLimit: The current block’s gas limit.
currentNumber: The current block’s number.
currentTimestamp: The current block’s timestamp.
previousHash: The previous block’s hash.

The exec Section¶

address: The address of the account under which the code is executing, to be returned by the ADDRESS instruction.
origin: The address of the execution’s origin, to be returned by the ORIGIN instruction.
caller: The address of the execution’s caller, to be returned by the CALLER instruction.
value: The value of the call (or the endowment of the create), to be returned by the CALLVALUE instruction.
data: The input data passed to the execution, as used by the CALLDATA… instructions. Given as an array of byte values. See $DATA_ARRAY.
code: The actual code that should be executed on the VM (not the one stored in the state(address)) . See $DATA_ARRAY.
gasPrice: The price of gas for the transaction, as used by the GASPRICE instruction.
gas: The total amount of gas available for the execution, as would be returned by the GAS instruction were it be executed first.

The pre and post Section¶

The pre and post sections each have the same format of a mapping between addresses and accounts. Each account has the format:

balance: The balance of the account.
nonce: The nonce of the account.
code: The body code of the account, given as an array of byte values. See $DATA_ARRAY.
storage: The account’s storage, given as a mapping of keys to values. For key used notion of string as digital or hex number e.g: "1200" or "0x04B0" For values used $DATA_ARRAY.

The callcreates Section¶

The callcreates section details each CALL or CREATE instruction that has been executed. It is an array of maps with keys:

data: An array of bytes specifying the data with which the CALL or CREATE operation was made. In the case of CREATE, this would be the (initialisation) code. See $DATA_ARRAY.
destination: The receipt address to which the CALL was made, or the null address ("0000...") if the corresponding operation was CREATE.
gasLimit: The amount of gas with which the operation was made.
value: The value or endowment with which the operation was made.

The logs Section¶

The logs sections contains the hex encoded hash of the rlp encoded log entries, reducing the overall size of the test files while still verifying that all of the data is accurate (at the cost of being able to read what the data should be). Each logentry has the format:

keccak(rlp.encode(log_entries))

(see https://github.com/ethereum/py-evm/blob/7a96fa3a2b00af9bea189444d88a3cce6a6be05f/eth/tools/_utils/hashing.py#L8-L16)

The gas and output Keys¶

Finally, there are two simple keys, gas and out:

gas: The amount of gas remaining after execution.
out: The data, given as an array of bytes, returned from the execution (using the RETURN instruction). See $DATA_ARRAY.

$DATA_ARRAY - type that intended to contain raw byte data

and for convenient of the users is populated with three types of numbers, all of them should be converted and concatenated to a byte array for VM execution.

The types are: 1. number - (unsigned 64bit) 2. “longnumber” - (any long number) 3. “0xhex_num” - (hex format number)

e.g: ````[1, 2, 10000, "0xabc345dFF", "199999999999999999999999999999999999999"]````