A set of Foundry rules for testing Ethereum smart contracts. Foundry is a toolkit for building and testing these blockchain programs, and TDD means writing a failing test before the code that makes it pass.

Use it to organize unit, integration, invariant, fork, fuzz, and exploit-proof tests for Solidity contracts.

It provides a consistent way to check normal behavior, failures, edge cases, gas use, and interactions with other contracts.

testing — Cursor rule by ccashwell

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add rules/ccashwell/evm-cortex/testing

Clone the repo

git clone --depth 1 https://github.com/ccashwell/evm-cortex

Made for: Cursor.

Per session 459 This file is loaded in full into every session.

When invoked 459 The same file — it is already loaded in full.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5	$0.00459	$0.00459
Opus 5	$0.00230	$0.00230
Sonnet 5	$0.00092	$0.00092
Haiku 4.5	$0.00046	$0.00046

Measured 2d ago against content hash 263a60551109, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

testing scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.cursor/rules/testing.mdc · 53 lines

What it actually says

Foundry Testing Standards

TDD Workflow

Write test first (RED) -- test must fail
Write minimal implementation (GREEN) -- test must pass
Refactor and optimize (IMPROVE)
Run forge snapshot to baseline gas
Target 90%+ coverage on critical paths

Test File Structure

test/
  unit/           # Unit tests per contract
  integration/    # Cross-contract interaction tests
  invariant/      # Stateful invariant tests
  fork/           # Fork tests against live protocols
  poc/            # Proof-of-concept exploit tests

Naming Conventions

Unit tests: test_FunctionName_Condition_ExpectedResult
Revert tests: test_RevertWhen_Condition
Fuzz tests: testFuzz_FunctionName_PropertyDescription
Invariant tests: invariant_PropertyDescription
Fork tests: testFork_ScenarioDescription

Test Quality Rules

Every public/external function must have at least one test
Test happy path AND failure cases
Test edge cases: 0, 1, type(uint256).max, empty arrays
Fuzz test ALL math operations (min 10,000 runs)
Fork-test ALL external protocol integrations
First depositor / last withdrawer scenarios for vaults
Invariant tests for core protocol properties

Cheatcode Usage

vm.prank(addr) for single-call impersonation
vm.startPrank(addr) / vm.stopPrank() for multi-call
deal(token, addr, amount) for token balances
vm.warp(ts) and vm.roll(bn) for time/block
vm.expectRevert(Error.selector) for revert tests
vm.expectEmit() for event verification
vm.assume() / vm.bound() for fuzz input constraints
makeAddr("name") for labeled test addresses

CI Integration

forge test --gas-report    # All tests + gas
forge snapshot --check     # Gas regression check
forge coverage             # Coverage report
slither .                  # Static analysis

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2d ago First seen · 53 lines · 459 tokens per session scan A 263a60551109

Subscribe to this mod's changes

testing is a cursor rule published in the GitHub repository ccashwell/evm-cortex (127 stars, last pushed 22d ago), licensed MIT. It adds 459 tokens to every session, about $0.0023 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Productivity Testing Writing and docs

testing

Getting it into your agent

What it costs to keep this loaded

Grade A, and why

Nothing flagged

What it actually says

Foundry Testing Standards

TDD Workflow

Test File Structure

Naming Conventions

Test Quality Rules

Cheatcode Usage

CI Integration

What this file has done since we first saw it

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