# M03-L03 — Lab contract

**Build:** Compare estimateGas, receipt.gasUsed, effectiveGasPrice.

**Pass:** Computed paid fee matches receipt fields where available.

**Failure injection:** Gas limit is not the same as gas spent; fees vary by network and tx type.

**Review question:** What happens to gas on revert?

Status: specification; only count as executable when source and tests are present and verified.