Nibiru Oracle Mocking Demo (Foundry)

🧩 What problem does this repo solve?

NibiruOracleChainlinkLike.latestAnswer() calls a Nibiru oracle precompile hard‑coded at 0x000…0801. On a local Foundry test‑VM this address has no code and no storage, so every call reverts with a custom error such as FeedNotFound("unibi:uusd").

🛠️ How we fixed it

1. OracleMock.sol – a minimal contract that implements the same ABI as the precompile (IOracle). It lets tests push arbitrary prices via setPrice(pair, price).
2. trick – Foundry cheat code used to copy the mock’s runtime bytecode into the real precompile slot.
3. Write storage after etch – because vm.etch transfers code only, the test calls OracleMock(PRECOMPILE).setPrice(...) after etching so the storage lives at the precompile address.

Result: your adapter contract reads prices just like on‑chain, and tests pass 🎉.

📁 Project structure

.
├── foundry.toml             # Foundry config
├── src/
│   ├── IOracle.sol          # Interface + global constants
│   ├── OracleMock.sol       # Mock that we etch
│   ├── NibiruOracleChainlinkLike.sol  # The adapter under test
│   └── ChainLinkAggregatorV3Interface.sol  # External interface
└── test/
    └── OraclePrecompile.t.sol  # Proof‑of‑concept test

🚀 Quick start

# 1) install Foundry once
curl -L https://foundry.paradigm.xyz | bash && foundryup

# 2) clone and test
forge install                               # pulls forge‑std
forge test -vvvv                           # should pass ✅

What you should see

[PASS] testLatestAnswer() (gas: …)

No EvmError: Revert, price equals 100e18.

🔍 Key lines to understand

// test/OraclePrecompile.t.sol
mock = new OracleMock();            // deploy standalone mock
vm.etch(PRECOMPILE, address(mock).code);  // move its *code* into 0x…0801
OracleMock(PRECOMPILE).setPrice("unibi:uusd", 100e18); // now write storage

feed = new NibiruOracleChainlinkLike("unibi:uusd", 18);

• Always set storage after the etch.

🧑‍💻 Extending

• Add more pairs: OracleMock(PRECOMPILE).setPrice("ubtc:uusd", 65000e18) * Need dynamic prices? Call setPrice inside each test or in beforeEach.
• Re‑use the base setup by inheriting from OraclePrecompileTest.

⚠️ Troubleshooting

Symptom	Likely cause
Revert with FeedNotFound	Price not set after etch
Zero price returned	Same as above, or wrong decimals
Identifier not found compile error	Missing import "./IOracle.sol";

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Made with ❤️ & vm.etch() so you can iterate fast.