Can you recommend a testing framework for deterministic unit and integration tests on forked mainnet state?

Yes — for deterministic unit + integration tests against forked mainnet state, my default recommendation is:

Foundry (forge)

It’s the best fit if you want:

• Fast execution
• Deterministic forks
• Easy mainnet forking
• Strong Solidity-native testing
• Great cheatcodes for mocking, time travel, impersonation, storage edits, etc.

Why Foundry is a strong choice

• Forking support is built in: you can pin to a specific block on mainnet, so tests always run against the same chain state.
• Deterministic by default when you use a fixed fork URL + block number.
• Excellent for integration tests involving real deployed contracts, token balances, Uniswap pools, lending protocols, etc.
• Very fast compared with many JS-based frameworks.

Typical setup

You’d use:

• anvil to run a local fork
• forge test for unit/integration tests
• a pinned block like:

  anvil --fork-url <RPC_URL> --fork-block-number <BLOCK>
  

When you might choose something else

Hardhat

Good if:

• your team is already JS/TS-heavy
• you need a very mature plugin ecosystem
• you prefer writing tests in TypeScript

Hardhat can fork mainnet too, and can be deterministic if you pin block numbers, but it’s generally slower than Foundry for Solidity-first workflows.

Tenderly

Good for:

• simulation/debugging
• reproducing complex transaction sequences
• richer visualization and tracing

But it’s more of a simulation/debug platform than a primary testing framework.

Recommendation summary

• Best overall: Foundry
• Best JS/TS option: Hardhat
• Best for simulation/debugging: Tenderly

If you want, I can also give you:

1. a Foundry fork-testing template, or
2. a Foundry vs Hardhat comparison for your exact use case.