Testing & Debugging

Essential guidance for testing Compact contracts, debugging common errors, and understanding compiler/runtime error messages.

Common Errors Quick Reference

Error Message	Likely Cause	Quick Fix
potential witness-value disclosure	Witness flows to public output	Add disclose() or use commitment
type mismatch	Incompatible types in operation	Check type signatures, use as for conversion
unbounded loop	Loop bounds not compile-time constant	Use literal or #N parameter for bounds
circuit constraint failed	Runtime assertion failed	Check assert conditions and inputs
proof generation failed	Invalid witness values	Verify witness function returns valid data
overflow	Arithmetic exceeds type bounds	Use larger Uint<N> or check bounds

Debugging Decision Tree

Error during compilation?
├── "potential witness-value disclosure"
│   └── See: references/error-messages.md#disclosure-errors
├── "type mismatch" or "cannot convert"
│   └── See: references/error-messages.md#type-errors
├── "unbounded loop" or "bounds must be constant"
│   └── See: references/error-messages.md#loop-errors
└── Other compilation error
    └── See: references/error-messages.md

Error during proof generation?
├── "assert failed" or "constraint failed"
│   └── Check assertion conditions and witness values
├── "proof generation failed"
│   └── Verify witness functions return expected types
└── "overflow" or "division by zero"
    └── Check arithmetic bounds

Testing Approaches

Unit Testing Circuits

import { TestContext } from '@midnight-ntwrk/compact-testing';

describe('MyContract', () => {
    let ctx: TestContext;

    beforeEach(async () => {
        ctx = await TestContext.create('my_contract.compact');
    });

    it('should process valid input', async () => {
        const result = await ctx.call('process', [42n]);
        expect(result.success).toBe(true);
    });
});

Witness Mocking

const mockWitness = {
    get_secret: () => BigInt('12345'),
    get_balance: () => BigInt(1000)
};

const result = await ctx.call('transfer', [recipient], mockWitness);

State Verification

// Read ledger state after circuit execution
const balance = await ctx.ledger.get('balances', userKey);
expect(balance).toBe(expectedBalance);

Common Pitfalls

Pitfall	Symptom	Solution
Forgetting disclose()	Compile error	Add explicit disclosure
Wrong ADT choice	Inefficient proofs	Use Counter for counting, MerkleTree for membership
Attempting unbounded loops	Compile error	Use bounded for i in 0..N
Uint overflow	Proof failure	Use larger bit width or check bounds
Division by zero	Proof failure	Add zero check before division

References

• Error Messages - Complete error reference with solutions
• Testing Strategy - Testing approaches and best practices
• Common Pitfalls - Frequent mistakes and how to avoid them

Examples

• Test Setup - TypeScript test harness configuration
• Mock Witnesses - Witness mocking patterns