test-generation-patterns

Test Generation Patterns

Generate comprehensive tests with AI assistance following 2026 best practices.

When to Use

• Adding tests to existing code
• Creating test suites for new features
• Improving test coverage
• Setting up testing patterns for a project
• Generating edge case tests

The Testing Pyramid (2026)

        ┌─────────┐
        │   E2E   │  Few, slow, high confidence
        ├─────────┤
        │ Integr. │  Some, medium speed
        ├─────────┤
        │  Unit   │  Many, fast, isolated
        └─────────┘

Unit Test Generation

Step 1: Identify Test Cases

For any function, test:

1. Happy path - Normal expected input
2. Edge cases - Boundaries, empty, null
3. Error cases - Invalid input, failures
4. State changes - If function has side effects

AI Prompt Template

Generate comprehensive unit tests for this function:

```[paste function]```

Include tests for:
1. Happy path with typical inputs
2. Edge cases (empty, null, boundary values)
3. Error handling
4. Any state changes or side effects

Use [Vitest/Jest/pytest] with [testing-library if applicable].
Follow AAA pattern (Arrange, Act, Assert).

Example: Testing a Utility Function

Code to test:

function parseAmount(input: string): number | null {
  if (!input || typeof input !== 'string') return null;
  const cleaned = input.replace(/[$,]/g, '').trim();
  const num = parseFloat(cleaned);
  return isNaN(num) ? null : Math.round(num * 100) / 100;
}

Generated tests:

import { describe, it, expect } from 'vitest';
import { parseAmount } from './parseAmount';

describe('parseAmount', () => {
  describe('happy path', () => {
    it('parses plain number', () => {
      expect(parseAmount('123.45')).toBe(123.45);
    });

    it('parses number with dollar sign', () => {
      expect(parseAmount('$99.99')).toBe(99.99);
    });

    it('parses number with commas', () => {
      expect(parseAmount('1,234.56')).toBe(1234.56);
    });