python-regression-test-generator

Python Regression Test Generator

Overview

This skill automatically generates regression tests for Python code by analyzing differences between old and new versions, migrating existing tests, and creating new tests for modified or added functionality. It ensures previously tested behavior still works while covering new code paths.

Test Generation Workflow

Follow these steps to generate regression tests:

1. Analyze Code Changes

Compare old and new versions to identify:

Function Signature Changes:

• Added parameters (with or without defaults)
• Removed parameters
• Changed parameter types or names
• Changed return types

Logic Changes:

• Modified implementation
• New validation rules
• Changed error handling
• Algorithm improvements

Structural Changes:

• Added functions/classes/methods
• Removed functions/classes/methods
• Renamed functions/classes/methods
• Moved code between modules

Example Analysis:

# Old version
def calculate_total(items):
    return sum(item.price for item in items)

# New version
def calculate_total(items, tax_rate=0.0):
    subtotal = sum(item.price for item in items)
    return subtotal * (1 + tax_rate)

Changes identified:

• Added parameter: tax_rate with default value 0.0
• Modified logic: now applies tax calculation
• Backward compatible: old calls still work

2. Analyze Existing Tests

Review old tests to understand:

• Test structure (unittest vs pytest)
• Test coverage (which functions/paths are tested)
• Test patterns (fixtures, mocks, parametrization)
• Dependencies and setup requirements

Example Existing Test:

def test_calculate_total():
    items = [Item(price=10), Item(price=20)]
    assert calculate_total(items) == 30

Analysis:

• Uses pytest style
• Tests basic functionality
• No mocking needed
• Simple assertion

3. Migrate Existing Tests

Update tests to work with new code:

For backward-compatible changes:

• Keep original test (ensures backward compatibility)
• Add new tests for new functionality