Synthetic Tests Generation (AI Writes Checks for Its Code)

1. Concept Overview & Systemic Problem

The greatest fear of any developer working with AI is: “Today I asked to add a dark theme to the site, and tomorrow I noticed that the payment button stopped working.” As a project grows, manually checking every button after each new generation becomes impossible.

Synthetic Tests Generation refers to the creation of automated audit programs. You provide the model with your function and instruct it:

“Write verification tests for this code that will check the 10 most insidious scenarios.”

Now the computer autonomously clicks all buttons, inputs incorrect passwords, checks calculations, and reports: “All 10 tests passed successfully!”

In practice, this serves as a solid foundation of peace: your project won't collapse from random AI edits.

2. Architectural Taxonomy & Mental Model

┌─────────────────────────────────────────────────────────────┐
│                 AUTOMATIC TEST GENERATION                  │
├─────────────────────────────────────────────────────────────┤
│ 1. Your function: `calculateDiscount(price, coupon)`        │
├─────────────────────────────────────────────────────────────┤
│ 2. Prompt: “Write Vitest tests for coupon verification”      │
├─────────────────────────────────────────────────────────────┤
│ 3. AI autonomously generates 4 critical scenarios:           │
│    ✓ Test 1: 10% discount on a 1000 UAH check ➔ should be 900 UAH  │
│    ✓ Test 2: Expired coupon ➔ throws an error               │
│    ✓ Test 3: Coupon gives a discount greater than the price ➔ check = 0 UAH  │
│    ✓ Test 4: Empty or invalid promo code ➔ no discount      │
├─────────────────────────────────────────────────────────────┤
│ 4. One-click execution in the terminal: `npm test` ➔ 100% PASS   │
└─────────────────────────────────────────────────────────────┘

3. Technical Pipeline & Internal Mechanics

Copy this prompt into your editor:

“Look at the file @src/utils/cart.ts. Write a complete set of unit tests for it using the Vitest library: 1. Cover positive standard scenarios. 2. Separately check edge cases: zero values, negative numbers, empty arrays, and incorrect types. 3. Save the result in the file @src/utils/cart.test.ts and write the command for execution in the terminal.”

4. Production Engineering Scenarios

01. Continuous Integration Testing

Integrate synthetic test generation into your CI/CD pipeline. Every code push triggers npm test, ensuring that AI-generated code modifications do not introduce regressions.

02. Rapid Prototyping

During rapid prototyping, leverage synthetic tests to validate new features quickly. Generate tests for new functionalities and run them to ensure stability before deployment.

03. Legacy Code Refactoring

When refactoring legacy code, use synthetic tests to create a safety net. Generate tests for existing functionalities to ensure that changes do not break any existing behavior.

5. Pitfalls, Common Mistakes & Security

Avoid relying solely on AI-generated tests without human oversight. Ensure that edge cases are comprehensively covered, as AI may overlook specific scenarios. Regularly review and update test cases to align with evolving project requirements and maintain security standards.