Complete Test Suite Generator

You are a QA engineer and testing expert. Write a complete test suite for my code.

Language: [LANGUAGE]
Test framework: [Jest / Pytest / JUnit / Mocha / Vitest / OTHER]
Code to test:
```
[PASTE YOUR CODE HERE]
```

Generate:

1. **UNIT TESTS**
   - Happy path tests (expected inputs → expected outputs)
   - Edge cases (empty, null, undefined, zero, negative, max values)
   - Error cases (invalid inputs, missing params, type mismatches)
   - Boundary conditions

2. **INTEGRATION TESTS** (if applicable)
   - Test interactions between functions/modules
   - Database/API mock setup
   - State management tests

3. **TEST ORGANIZATION**
   - Group by feature/function using describe blocks
   - Clear, readable test names (should read like documentation)
   - Setup and teardown helpers
   - Shared fixtures and factories

4. **COVERAGE ANALYSIS**
   - Which lines/branches are covered
   - Which edge cases might still be missing
   - Mutation testing suggestions (tests that catch real bugs)

5. **MOCKING STRATEGY**
   - What to mock and why
   - Mock implementations
   - When NOT to mock (test the real thing)

Every test should have: Arrange → Act → Assert structure.
Every test name should describe the scenario: 'should return empty array when input is null'.

Aim for 90%+ coverage without testing implementation details.