Lesson 25: Advanced Bot Testing (Simulations, Edge Cases & Fuzzing)

In this lesson, you will learn how to rigorously test your Forta agents, ensuring they perform reliably under real-world conditions. For that we will go deeper into simulation, edge case testing, and fuzzing, which are all essential tools to make your bot a resilient guardian on-chain.

---

Understanding Bot testing easier

Imagine training a guard dog.

You don’t just show it one burglar.
You test it with disguises, distractions, and weird edge cases.

Well, same for your detection bots.

You must simulate not just the “happy path,” but also attackers trying to break through unseen places.

---

Why Advanced Testing is important

Forta bots must:

• Detect real issues without triggering false alarms

• Safely process incomplete or invalid input.

• Avoid false positives in strange conditions

• Survive updates, reorgs, edge chains, and MEV chaos

Robust testing makes sure your bot can manage unexpected scenarios smoothly.

---

Types of Advanced Tests

---

Simulating Real Transactions

Use Forta’s CLI to replay actual Ethereum data into your bot.

npx forta-agent simulate \
  --tx 0x5fbb4592... \
  --agent-path ./src \
  --json

Why It Helps:

• Reproduces real on-chain behavior

• Lets you test alerts for known exploits

• Ideal for verifying that existing features still work after changes

---

Designing Edge Cases

Think like an attacker and ask yourself:

• What if value is 0?

• What if from === to?

• What if a contract emits no logs but performs internal changes?

• What if gas used is just below the threshold?

Example:

handleTransaction(tx) {
  if (tx.value === "0") {
    findings.push(
      Finding.fromObject({
        name: "Zero Value Tx",
        description: "Might be suspicious dusting behavior",
        alertId: "ZERO-TX",
        severity: Severity.Low,
        type: FindingType.Suspicious,
        metadata: { txHash: tx.hash }
      })
    );
  }
}

Create unit tests for every edge you can think of.

---

Fuzz Testing (Randomized Inputs)

Use tools to generate large volumes of random, malformed, or boundary-pushing inputs.

While Forta CLI doesn’t yet support full fuzzing, you can:

• Write scripts that generate 1,000+ fake txs

• Randomize sender, receiver, value, gas, etc.

• Pass the alerts into your handler functions

Helpful npm libraries:

• faker

• chance

• fast-check

Fuzz testing can expose failures, inefficiencies, or noisy alert behavior

---

Testing Structure Example

Here's a simple project structure for strong testing:

/src
  agent.js
/test
  agent.test.js
  edge-cases.test.js
  simulations/
    tx-replay-1.json
    tx-replay-2.json
/fuzz
  generate-fake-txs.js

Include scripts to run all test suites before deployment.

---

Gas Consumption

Don't forget to measure how expensive your logic is.

npx forta-agent simulate \
  --tx 0xabc... \
  --measure-performance

If you’re iterating over too many logs or parsing complex ABI structures then refactor.

---

Key Concepts Recap

• Simulation involves replaying real txs to test expected behavior

• Edge Case testing means feeding weird, rare, malformed inputs

• Fuzzing involves applying brute force testing with randomized inputs

• Advanced testing protects your bot from false positives, false negatives, and crashes

• Use CLI tools and custom scripts to automate test coverage

Next lesson, we will explore building multi-chain monitoring strategies, because DeFi threats don’t stay on one chain.

🙏 Until next meditation,
The Blockchain Security Monk