How to mock web3 provider for unit test?

[boldchains]

[ricmoo]

I need more information to go on for this issue.

Also, moving to discussions.

[viztor]

There is currently no way to write unit test for app using ether.js, you have of course mock functions one by one, hoping there could be some mock provider that does all the stuff.

[boldchains]

My apologies, we are using ethers.js for specific crypto exchange project, and we are plan to write unit tests over all the project. Unfortunately, I don't see preferred mocking packages for ether.js. Do you have any suggestion for this purpose?

[dimitardanailov]

@ricmoo

I've a question: What's is your recommendation for version 6 (2023 edition) ?

My implementation is:

import {JsonRpcProvider} from 'ethers'

class MockProvider extends JsonRpcProvider {
  async getBlockNumber(): Promise<number> {
    return 1337
  }
}

export default MockProvider

[adridadou]

Hey everyone, I know I come a bit late to the party but I have a question regarding that and I cannot find an answer anywhere. I've been working on a FakeProvider that works fairly well. I can mock smart contract calls among other things.

The issue I have is, how do I mock a failure ? I tried to throw an error but that does not seem to be working. so I am trying to figure out what the format should be to make it work.

happy to give more details if this is unclear and once I'm done let me know if anyone would be interested to have it. Love to share

[ricmoo]

@adridadou What type of failure? You should be able to use the assert from the utils, which takes in all the necessary parameters to throw; it’s all that the existing providers use.

If you create a FakeProvider, let me know and I can link to it from the docs. :)

[ricmoo]

@dimitardanailov Btw, the main advantage of doing everything in perform is that the bare methods like getBlock and what it do a lot of normalizing for you, such as converting a negative block number into the absolute block number, make sure addresses are formatted properly, etc.

[adridadou]

I figured it out. I wanted to simulate a reverted call. The way to do it is to prefix your error message with "reverted:" and then return it. The code recognizes this and converts it into a failed call.

Regarding adding the FakeProvider to the docs, should I create a lib or can I make a PR here ? I want others to find it quickly and also improve on it if necessary

[zemse]

@james-lin71 you may be interested in mainnet forks provided by hardhat's node. You may also find the Hardhat + Waffle combination great, as it provides you to create a MockProvider for use in unit tests.