# Is it possible to test contract with bytecode only?

##background I only have the bytecode of the contract, and bytecode-level constuctor for the contract. I want to deploy the contract to my local private chain and invoke some methods to run my test logic on the contract. At first, I was thinking about geth, and have done a lot of preperation. But later I realised that it is acutally not necessary to use geth, testrpc or ganache-cli can make some of the parts more convenient: No need to create accounts, and transfer ETH between accounts, no need to mine the transactions anymore….etc. At last my solution is to write a web3 script, and interact with the ganache-cli chain on my local machine.

## Deployment

I successfully deployed the contract with the guidance of this answer. The deployment process is a transaction, and the parameters is explained here.

eth.sendTransaction({from:eth.accounts[0],to:"0x0000000000000000000000000000000000000000",value:0,data:storageBincode})


storageBincode here represents the bytecode of the contract, but we should note that the bytecode here should be (contract bytecode + constructor bytecode). This blog shows the hard way to deploy smart contract. At first I thought that the ABI file is always needed for deployment, but as we didn’t provide the abi data, so contractAddress here is null. However, This answer by Ismael explained the reason, by removing the to parameter, I got the contractAddress.

## Call methods

The answers under this question reveals the method to call a function. However, the method implemented in the blog is in solidity, bytes4(keccak256("f1(arg1_type, arg2_type)") As there are just a few methods used in this test, there is no need to calculate them. This link can get the signature encoded from function string

### Transaction

sendTransaction method in web3 have these arguments: from, to, value,gas, data. As for how to fill these values, we can first test the certain contract on Remix, then we can learn the information from the receipt.

### Call

Note that, call methods are much different from transactions, sendTransaction can only return the hash value of the transaction, while in order to get the return value from call method, we have to implement eth.call(to:, data:,).

## Testing

### How do I construct my testing code?

First, it is quite important to import the json file, which contains the bytecode information for every contract to be tested. SyntaxError: Unexpected token } in JSON at position 93 This error keeps showing up in all forms. At last I found out that this has something to do with my json file, (I thought there are something wrong with npm at first because it is about JSON.) At last I found out that, My json file is constructed like this: a:. So there is one comma more than normal, which lead to the error.

### Etherscan analysis

The bytecode information can be divided into two types on etherscan. When source code is available, the bytecode is creation-bytecode, which means the value of constructor arguments have already been attached to it. The other type is those which source code is not available, the bytecode of the contract and consturctor are seperated.

### Async/await/then/promise/callback

Actually this is quite an easy thing to do—-if I am familiar with javascript, sadly, I don’t, and it’s quite hard. I struggled a lot from these things: async/await

A guide to promise in web3 ### I tried to paste an already deployed address to the to field and it works. However, the current code keeps reverting and I can not understand why.

var setupTransferReceipt = await web3.eth.sendTransaction({from:accounts[0].toLowerCase(),to:token_address.toLowerCase(),value:0,data:setupBinCode},function(error,hash){if (error)console.log(hash)});

var setupTransferReceipt = await web3.eth.sendTransaction({from:accounts[0].toLowerCase(),to:'0xc437E6cb41e8432766c37577bBDbC4F98b5Bd78e'.toLowerCase(),value:0,data:setupBinCode},function(error,hash){if (error)console.log(hash)});


Here setupBinCode is the data previously defined, token_address is obtained from the previously deployed token. So I think there are some possibilities to this error:

• token_address is null

=> I added web3.eth.getTransaction(tokenDeploymentReceipt.transactionHash) .then(console.log); and it turns out that this is not the problem, when console.log(token_address), the corresponding address is printed.

• type of token_address is not correct.

=> After several test, I found out that string type is required in to field, but that’s exactly what I have passed into it!!

• to field require lower case?

=> The address I pasted obtained from log field was all in lowercase, so I think this might be one of the problem, but it turns out NO.

｡°(°¯᷄◠¯᷅°)°｡ So what on earth is the problem?

Async issue

### How to write/read json file in javascript

#### Write

var fs = require('fs')
var FileSaver = require('file-saver')
var jsonfile = require('jsonfile')
var file = ''
var keys = Object.keys(parsed)



### How to use regular expression in js?

I raised this question because I wanted to delete 0x in the address string, it turns out that it’s quite similar as in python: string.replace('What you want to replace','')

### Type of arguments

At first I wrote var token_address = tokenDeploymentReceipt.contractAddress But when I implemented the transfer method in the contract, it keeps revert, after several test, I found out that there might be something wrong with

npm install file-saver --save
bower install file-saver


### This works in node console, but won’t work if I put these in a .js file and run it, keeps telling me that accounts is undefined

var accounts
async function getCurrentAccount()
{
accounts = await web3.eth.getAccounts();
return accounts;
}
getCurrentAccount()


return promise problem

## issues

### Geth part(not implemented)

#### Geth parameter

There are some parameters that have to be pre-set to the geth when it started.

• With script --exec 'loadScript("/home/jiru/桌面/mine_transactions.js")'
• UnlockAccount

geth --rpc --nodiscover --datadir data0 --port 30303 --rpc --allow-insecure-unlock --rpcport 8545 --rpcapi "db,eth,net,web3" --rpccorsdomain "*" --networkid 1108 --ipcdisable --exec 'loadScript("/home/jiru/桌面/mine_transactions.js")' console

#### Ethereum Script

I found a repository in github with many scripts that can be used in geth and make things easier. This problem was raised by: How to make miner to mine only when there are Pending Transactions? But later I found out that in my case it’s much easier to use ganache-cli instead of geth which make everything easier XD. One excellent blog

#### eth not defined

I didn’t create an web3 instance. eth is part of web3. create it like this.

const Web3 = require('web3')
const web3 = new Web3('http://localhost:8545')


Then this will disappear.

#### Speed

The speed is so low that I thought there are something about the statement in the console. npm: request has been deprecated How smart contract deployment works

#### genesis.json

##### miner.start(1) hangs forever

Actually, two weeks ago when I was doing my homework, miner.start(1) hangs forever. parameter explain At first I didn’t understand how geth works, and was certain that there must be something wrong with installation, after install & uninstall, I pathetically found out that this is a rather silly way to try to solve any problem. Take the time to look into documentation or copy and paste the error information on Google is much more better. Later I found out that "eip150Block" field is blank in genesis.json. However, I don’t know why this helps yet.

##### No status field in receipt

I need to know the status of the transaction, however, Geth uses Web3 with version lower than 1.0.0, and this is a known bug in the earlier version as presented in this issue

I created an issue on geth github page, and got one response, but web3 version is one reason, later I found out another issue mentioning that when block number < 4700000 there will not be status field. This number reminds me of Byzantium. This blog is extremely clear and I learned from it that only if I set the parameter ByzantiumBlock in genesis.json, then there will be status field in the receipt. Because this field shows up after Byzantium. This is the docs for web3 utilized in geth. Geth docs

#### gas required exceeds allowance&exceeds block gas limit

I want to send a transaction. var result = eth.estimateGas({from:eth.accounts[1],to:contractAddress,value:0,data:"0xa9059cbbabbbd78b61fd39cb518e08b41fdd3fe9af8ade1d0000000000000000000000000000000000000000000000000000000000000074"}) returns 51165. However, when I tried to send this transaction, here comes this error: gas required exceeds allowance (16276726) or always failing transaction This result from revert.

#### exceed block gas limit

How to edit block gas limit Hoever, I got an error, saying Cannot find module 'ganache-cli' This is the only solution I found online.

## Conclusion

My feeling when I have to finish this within a short period time without any knowledge of javascript: