Edge-Case Driven Unit Test Suite Generator with Mocks
Generate thorough, resilient unit test suites targeting boundary conditions, error branches, and mock contracts.
Compatibility & Specs
Compatible AI Models
ClaudeChatGPTGemini
Last UpdatedOct 3, 2026
Customizable Variables3 parameters
Main Prompt Template
146 words • 1110 characters
You are a Principal Software Quality Engineer and Test-Driven Development (TDD) Advocate. I need a production-grade unit test suite for a function or class that covers critical edge cases and failure modes.
Target Code to Test:
[code_to_test]
Testing Framework & Language:
[testing_framework]
Dependencies or Side Effects (APIs, Database, Clocks, Environment):
[external_dependencies]
Generate an exhaustive Unit Test Suite:
1. Boundary Condition & Edge Case Inventory: Table listing the edge cases to verify (e.g. Empty collections, Null/Undefined inputs, String encoding, Max integer limits, Negative values, Network timeouts).
2. AAA-Structured Test Code: Write production-ready test code following the Arrange-Act-Assert pattern with clean descriptive test titles (`it('should throw RateLimitError when token bucket is exhausted')`).
3. Mocking & Isolation Strategy: Mock external side effects cleanly (using spies or stub factories) without over-mocking internal implementation details.
4. Negative Testing & Invariant Assertions: Ensure every error branch and custom exception is explicitly asserted.
Tip:Variables marked in purple brackets can be tailored below.
Customize Prompt
Fill in the variables below. Your customized prompt updates instantly in the browser — no AI API needed.
Parameters (3)* Indicates required field
[code_to_test]
The function, class, or module to test
[testing_framework]
Vitest/Jest with TypeScript, PyTest with Python, etc.
[external_dependencies]
What needs to be mocked or stubbed
3 parameters active
Live Customized OutputLive Preview
210 wordsYou are a Principal Software Quality Engineer and Test-Driven Development (TDD) Advocate. I need a production-grade unit test suite for a function or class that covers critical edge cases and failure modes.
Target Code to Test:
export async function transferFunds(fromAccountId: string, toAccountId: string, amountCents: number, ledger: LedgerClient): Promise<TransferResult> {
if (amountCents <= 0) throw new InvalidAmountError('Amount must be positive');
if (fromAccountId === toAccountId) throw new SameAccountError('Cannot transfer to same account');
const balance = await ledger.getBalance(fromAccountId);
if (balance < amountCents) throw new InsufficientFundsError('Overdraft limit reached');
return await ledger.executeAtomicTransfer(fromAccountId, toAccountId, amountCents);
}
Testing Framework & Language:
Vitest with TypeScript and vi.mock.
Dependencies or Side Effects (APIs, Database, Clocks, Environment):
LedgerClient interface with getBalance(accountId) and executeAtomicTransfer(from, to, amount).
Generate an exhaustive Unit Test Suite:
1. Boundary Condition & Edge Case Inventory: Table listing the edge cases to verify (e.g. Empty collections, Null/Undefined inputs, String encoding, Max integer limits, Negative values, Network timeouts).
2. AAA-Structured Test Code: Write production-ready test code following the Arrange-Act-Assert pattern with clean descriptive test titles (`it('should throw RateLimitError when token bucket is exhausted')`).
3. Mocking & Isolation Strategy: Mock external side effects cleanly (using spies or stub factories) without over-mocking internal implementation details.
4. Negative Testing & Invariant Assertions: Ensure every error branch and custom exception is explicitly asserted.
How to Use This Prompt
Follow this 3-step workflow to extract high-signal responses from any compatible AI model.
01
1. Tailor the Parameters
Use the interactive customizer above to substitute the bracketed placeholders with your exact context, requirements, and constraints.
02
2. Send to AI Model
Copy the prompt and paste it into Claude, ChatGPT, Gemini, or Copilot. These models follow structured multi-step constraints reliably.
03
3. Review and Iterate
Review the output against the verified benchmark below. Follow up in the conversation to stress-test edge cases or refine tone.
Prompt Variables & Parameters
Reference breakdown of every dynamic variable embedded in this prompt template.
| Placeholder | Parameter Name | Type | Status | Description & Guidance |
|---|---|---|---|---|
| [code_to_test] | Code to Test | textarea | Required | The function, class, or module to testDefault: export async function transferFunds(fromAccountId: string, toAccountId: string, amountCents: number, ledger: LedgerClient): Promise<TransferResult> { if (amountCents <= 0) throw new InvalidAmountError('Amount must be positive'); if (fromAccountId === toAccountId) throw new SameAccountError('Cannot transfer to same account'); const balance = await ledger.getBalance(fromAccountId); if (balance < amountCents) throw new InsufficientFundsError('Overdraft limit reached'); return await ledger.executeAtomicTransfer(fromAccountId, toAccountId, amountCents); } |
| [testing_framework] | Testing Framework & Language | text | Required | Vitest/Jest with TypeScript, PyTest with Python, etc.Default: Vitest with TypeScript and vi.mock. |
| [external_dependencies] | Dependencies & External Clients | text | Required | What needs to be mocked or stubbedDefault: LedgerClient interface with getBalance(accountId) and executeAtomicTransfer(from, to, amount). |
Example Execution & Benchmark Output
Sample input arguments and the verified AI response demonstrating expected quality and formatting.
Sample VariablesInputs
[code_to_test]
export async function transferFunds(fromAccountId: string, toAccountId: string, amountCents: number, ledger: LedgerClient): Promise<TransferResult> {
if (amountCents <= 0) throw new InvalidAmountError('Amount must be positive');
if (fromAccountId === toAccountId) throw new SameAccountError('Cannot transfer to same account');
const balance = await ledger.getBalance(fromAccountId);
if (balance < amountCents) throw new InsufficientFundsError('Overdraft limit reached');
return await ledger.executeAtomicTransfer(fromAccountId, toAccountId, amountCents);
}
[testing_framework]
Vitest with TypeScript and vi.mock.
[external_dependencies]
LedgerClient interface with getBalance(accountId) and executeAtomicTransfer(from, to, amount).
Expected AI ResponseVerified Result
### Edge-Case Matrix & Vitest Suite
```typescript
import { describe, it, expect, vi, beforeEach } from 'vitest';
import { transferFunds } from './transfer';
import { InvalidAmountError, SameAccountError, InsufficientFundsError } from './errors';
describe('transferFunds()', () => {
let mockLedger: any;
beforeEach(() => {
mockLedger = {
getBalance: vi.fn(),
executeAtomicTransfer: vi.fn(),
};
});
describe('Input Validations', () => {
it('should throw InvalidAmountError when amount is zero or negative', async () => {
await expect(transferFunds('acc-1', 'acc-2', 0, mockLedger))
.rejects.toThrow(InvalidAmountError);
await expect(transferFunds('acc-1', 'acc-2', -500, mockLedger))
.rejects.toThrow(InvalidAmountError);
expect(mockLedger.getBalance).not.toHaveBeenCalled();
});
it('should throw SameAccountError when sender and recipient are identical', async () => {
await expect(transferFunds('acc-1', 'acc-1', 1000, mockLedger))
.rejects.toThrow(SameAccountError);
});
});
describe('Balance & Execution Branches', () => {
it('should throw InsufficientFundsError when balance is less than transfer amount', async () => {
mockLedger.getBalance.mockResolvedValue(499);
await expect(transferFunds('acc-1', 'acc-2', 500, mockLedger))
.rejects.toThrow(InsufficientFundsError);
expect(mockLedger.executeAtomicTransfer).not.toHaveBeenCalled();
});
it('should successfully transfer when balance exactly equals amount', async () => {
mockLedger.getBalance.mockResolvedValue(500);
mockLedger.executeAtomicTransfer.mockResolvedValue({ status: 'COMPLETED', txId: 'tx-99' });
const result = await transferFunds('acc-1', 'acc-2', 500, mockLedger);
expect(result.status).toBe('COMPLETED');
expect(mockLedger.executeAtomicTransfer).toHaveBeenCalledWith('acc-1', 'acc-2', 500);
});
});
});
```
Best Use Cases
Scenarios and roles where this prompt produces maximum leverage.
Developers generating complete edge-case test suites for critical financial or business logic
Teams improving test coverage to meet strict CI/CD pull request gate requirements
Engineers refactoring critical code with full regression test safety nets
Tips for Best Results
Techniques to elevate response fidelity
- •Provide rich background context rather than one-sentence inputs to receive deep, non-generic responses.
- •Engage in multi-turn conversation: use the initial output as a baseline, then ask the AI to sharpen specific sections.
- •Prompt the model to highlight any hidden assumptions or missing trade-offs in its recommendations.
Common Mistakes to Avoid
Frequent failure modes and anti-patterns
- •Giving minimal context and expecting nuanced, expert-level strategic output.
- •Not validating factual references, citations, or statistical claims with verified primary sources.
- •Skipping the customization step and pasting raw bracketed template variables into the AI chat.
Part of Curated Collections
This prompt is sequenced as part of these goal-oriented workflows
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