[good first issue] Golden-file tests for intent decoders (Across + UniswapX)

[abhicris]

Context

The Across decoder (src/intents/across.rs, PR #3) has a decode_deposit_event pure-function entry point that's perfect for golden-file testing, but right now our coverage is shallow. Agents downstream of resolver trust the decoder to produce stable, normalized Intents — we should lock that behavior with fixture-based tests that fail loudly if the decoder's output drifts.

Scope

• Create tests/fixtures/ at repo root.
• For each supported decoder (Across, UniswapX), capture 3 real JSON fixtures:
  • tests/fixtures/across_v3_deposit_eth_to_arb.json — a real V3FundsDeposited event JSON (you can pull one from Etherscan logs or the Across subgraph).
  • tests/fixtures/across_v3_deposit_base_to_arb.json
  • tests/fixtures/across_v3_expired.json — one where fill_deadline < now, to pin expiry-handling behavior.
  • Corresponding UniswapX fixtures for mainnet and Arbitrum.
• For each fixture, create a matching <name>.expected.json that captures the normalized Intent output (pretty-printed JSON). These become golden files.
• Add tests/intent_decoders.rs that:
  1. Loads each fixture.
  2. Runs it through the decoder.
  3. Serializes the resulting Intent with serde_json::to_string_pretty.
  4. Asserts == against the .expected.json.
• Document fixture format in tests/fixtures/README.md so future decoders can add their own.

Acceptance criteria

• cargo test --test intent_decoders green.
• cargo clippy --tests clean.
• If a contributor breaks decoder output, the failing diff is human-readable (use pretty_assertions crate — add as dev-dep).
• At least 6 fixtures total across the two decoders.

Reference: src/intents/across.rs decode_deposit_event, and PR #3 for the testing conventions already in place.

Estimated effort

S (4–6 hours) — the work is collecting real data and committing the goldens.

— kcolbchain / Abhishek Krishna

[abhicris]

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