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
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