Foundry Testing & Script Skill

Rules and patterns for Foundry tests. Find examples in the actual codebase.

Bundled References

Reference	Content	When to Read
.claude/skills/foundry-testing/references/test-infrastructure.md	Constants, defaults, mocks	When setting up tests
.claude/skills/foundry-testing/references/cheat-codes.md	Common cheatcode patterns	When using vm cheatcodes
.claude/skills/foundry-testing/references/invariant-patterns.md	Handlers, stores, invariants	When writing invariant tests
.claude/skills/foundry-testing/references/formal-verification.md	Halmos, Certora, symbolic exec	When proving correctness
.claude/skills/foundry-testing/references/deployment-scripts.md	Script patterns, verification	When writing deploy scripts
.claude/skills/foundry-testing/references/deployment-checklist.md	Pre-mainnet deployment steps	Before deploying to production
.claude/skills/foundry-testing/references/gas-benchmarking.md	Snapshot, profiling, CI	When measuring gas performance
.claude/skills/foundry-testing/references/sablier-conventions.md	Sablier-specific patterns	When working in Sablier repos

---

Test Types

Type	Directory	Naming	Purpose
Integration	tests/integration/concrete/	*.t.sol	BTT-based concrete tests
Fuzz	tests/integration/fuzz/	*.t.sol	Property-based testing
Fork	tests/fork/	*.t.sol	Mainnet state testing
Invariant	tests/invariant/	Invariant*.t.sol	Stateful protocol properties
Scripts	scripts/solidity/	*.s.sol	Deployment/initialization

---

1. Integration Tests (Concrete)

Naming Convention

Pattern	Usage
test_RevertWhen_{Condition}	Revert on input
test_RevertGiven_{State}	Revert on state
test_When_{Condition}	Success path

Rules

1. Stack modifiers to document BTT path (modifiers are often empty - just document the path)
2. Expect events BEFORE action - vm.expectEmit() then call function
3. Assert state AFTER action - Check state changes after function executes
4. Use revert helpers for common patterns (expectRevert_DelegateCall, expectRevert_Null)
5. Named parameters in assertions - assertEq(actual, expected, "description")

Mock Rules

1. Place all mocks in tests/mocks/
2. One mock per scenario (not one mega-mock)
3. Naming: *Good, *Reverting, *InvalidSelector, *Reentrant

---

2. Fuzz Tests

Naming Convention

testFuzz_{FunctionName}_{Scenario}

Rules

1. Bound before assume - _bound() is more efficient than vm.assume()
2. Bound in dependency order - Independent params first, then dependent
3. Never hardcode params with validation constraints
4. Document fuzzed scenarios in NatSpec

Bounding Pattern

// 1. Bound independent params first
cliffDuration = boundUint40(cliffDuration, 0, MAX - 1);

// 2. Bound dependent params based on constraints
totalDuration = boundUint40(totalDuration, cliffDuration + 1, MAX);

---

3. Fork Tests

Rules

1. Create fork with vm.createSelectFork("ethereum")
2. Use deal() to give tokens to test users
3. Use assumeNoBlacklisted() for USDC/USDT
4. Use forceApprove() for non-standard tokens (USDT)

Token Quirks

Token	Issue	Solution
USDC/USDT	Blacklist	assumeNoBlacklisted()
USDT	Non-standard	forceApprove()
Fee-on-transfer	Balance diff	Check actual received amount

---

4. Invariant Tests

Architecture

tests/invariant/
├── handlers/     # State manipulation (call functions with bounded params)
├── stores/       # State tracking (record totals, IDs)
└── Invariant.t.sol

Rules

1. Target handlers only - targetContract(address(handler))
2. Exclude protocol contracts - excludeSender(address(vault))
3. Use stores to track totals for invariant assertions
4. Early return in handlers if preconditions not met

---

5. Solidity Scripts

Rules

1. Inherit from BaseScript with broadcast modifier
2. Use env vars: ETH_FROM, MNEMONIC
3. Simulation first, then broadcast

Commands

# Simulation
forge script scripts/Deploy.s.sol --sig "run(...)" ARGS --rpc-url $RPC

# Broadcast
forge script scripts/Deploy.s.sol --sig "run(...)" ARGS --rpc-url $RPC --broadcast --verify

---

Running Tests

# By type
forge test --match-path "tests/integration/concrete/**"
forge test --match-path "tests/fork/**"
forge test --match-contract Invariant_Test

# Specific test
forge test --match-test test_WhenCallerRecipient -vvvv

# Fuzz with more runs
forge test --match-test testFuzz_ --fuzz-runs 1000

# Coverage
forge coverage --report lcov

---

Debugging

Verbosity Levels

Flag	Shows
-v	Logs for failing tests
-vv	Logs for all tests
-vvv	Stack traces for failures
-vvvv	Stack traces + setup traces
-vvvvv	Full execution traces

Console Logging

import { console2 } from "forge-std/console2.sol";

console2.log("value:", someValue);
console2.log("address:", someAddress);
console2.logBytes32(someBytes32);

Debugging Commands

# Trace specific failing test
forge test --match-test test_MyTest -vvvv

# Gas report for a test
forge test --match-test test_MyTest --gas-report

# Debug in interactive debugger
forge debug --debug tests/MyTest.t.sol --sig "test_MyTest()"

# Inspect storage layout
forge inspect MyContract storage-layout

Debugging Tips

1. Label addresses - vm.label(addr, "Recipient") for readable traces
2. Check state with logs - Add console2.log before reverts
3. Isolate failures - Run single test with --match-test
4. Compare gas - Use --gas-report to spot unexpected costs
5. Snapshot comparisons - Use vm.snapshot() / vm.revertTo() to isolate state changes

---

Best Practices Summary

1. Use constants from Defaults/Constants - never hardcode
2. Specialized mocks - one per scenario, all in tests/mocks/
3. Modifiers in Modifiers.sol - centralize BTT path modifiers
4. Label addresses with vm.label() for traces
5. Events before actions - vm.expectEmit() then call
6. Bound before assume - more efficient

External References

• Foundry Book

---

Example Invocations

Test this skill with these prompts:

1. Integration test: "Write a concrete test for withdraw that expects Errors.Flow_Overdraw when amount exceeds balance"
2. Fuzz test: "Create a fuzz test for deposit that bounds amount between 1 and type(uint128).max"
3. Fork test: "Write a fork test for USDC deposits on mainnet with blacklist handling"
4. Invariant test: "Create an invariant handler for the deposit and withdraw functions"
5. Deploy script: "Write a deployment script for SablierFlow with verification"