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VM test

Found in vmtests.json, the VM tests aim is to test the basic workings of the VM in isolation. 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.

It 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) as well as any output returned from the code (output) is also detailed.

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 potion 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.

It is generally expected that the test implementer will read env, exec and pre then check their results against gas, out, post and callcreates.

Basic structure

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

Sections

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.
• 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 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.
• storage: The account's storage, given as a mapping of addresses to values.

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.
• 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.

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

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