Add chex.variants pytest example

[Sikandar1310291]

Overview

This PR adds a comprehensive example file demonstrating how to properly use chex.variants with parametrization in pytest. This addresses a common confusion point for users trying to combine chex.variants with test parametrization.

Motivation

Many users encounter issues when attempting to use pytest.mark.parametrize with chex.TestCase because:

• chex.variants requires test classes to inherit from chex.TestCase (which uses unittest.TestCase)
• pytest.mark.parametrize does NOT work with unittest.TestCase subclasses
• There was no clear documentation showing the correct pattern

Related to issue #382

What's Included

The new file chex/_src/variants_pytest_example.py contains four complete test class examples:

1. TestBasicVariants

• Basic variant usage without parametrization
• Demonstrates @chex.variants with with_jit and without_jit
• Shows how to use @self.variant decorator

2. TestCombinedParametrize

• CRITICAL: Shows that @chex.variants MUST be the OUTSIDE decorator (applied first)
• Demonstrates using absl.testing.parameterized (which works with unittest)
• Examples with single and multiple parameters
• Shows named parameters for better test identification

3. TestMultipleVariants

• Examples using multiple variant types simultaneously
• More complex variant combinations

4. Additional examples

• Advanced patterns and edge cases

Key Takeaways

✅ DO: Use absl.testing.parameterized with chex.variants
❌ DON'T: Use pytest.mark.parametrize with chex.TestCase
⚠️ IMPORTANT: @chex.variants must be the outer decorator

Usage

Run the examples with:

pytest chex/_src/variants_pytest_example.py -v

Testing

All examples have been tested and run successfully with pytest, demonstrating the correct patterns for combining variants with parametrization.

Checklist

• Added comprehensive example file with 217 lines of code
• Includes 4 different test class patterns
• Documented the critical decorator ordering requirement
• Provided clear usage instructions
• All examples are functional and tested