fix: rename tests/vendor to tests/test_vendor to avoid import conflicts

The tests/vendor/ directory was conflicting with src/vendor/ in pytest's
import resolution. When pytest added tests/ to sys.path, it would import
tests/vendor/__init__.py instead of src/vendor/__init__.py, causing all
vendor imports to fail.

Renaming to tests/test_vendor/ fixes this conflict and allows tests to run.

Also updated test infrastructure:
- Enhanced tests/conftest.py with pytest_configure hook
- Added README_TESTS.md with instructions for running tests locally
- Removed redundant tests/vendor/conftest.py

All 6 catalog extra fields tests now pass successfully.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: jontsai

README_TESTS.md

@@ -0,0 +1,62 @@
+# Running Tests
+
+## Quick Start
+
+The easiest way to run the catalog extra fields tests:
+
+```bash
+# Activate virtual environment
+source .venv/bin/activate
+
+# Run catalog extra fields tests
+python -m pytest tests/test_vendor/test_catalog_v1.py -v
+```
+
+## All Test Commands
+
+```bash
+# Run all catalog vendor tests
+python -m pytest tests/test_vendor/ -v
+
+# Run specific test file
+python -m pytest tests/test_vendor/test_catalog_v1.py -v
+
+# Run specific test class
+python -m pytest tests/test_vendor/test_catalog_v1.py::TestMetadataExtraFields -v
+
+# Run specific test method
+python -m pytest tests/test_vendor/test_catalog_v1.py::TestMetadataExtraFields::test_metadata_accepts_extra_fields -v
+
+# Run with more verbose output
+python -m pytest tests/test_vendor/test_catalog_v1.py -vv
+
+# Run and show print statements
+python -m pytest tests/test_vendor/test_catalog_v1.py -v -s
+
+# Run all tests in the project
+python -m pytest tests/ -v
+```
+
+## Using tox (Recommended for full test suite)
+
+The GitHub Actions CI uses tox to run tests across multiple Python and Pydantic versions:
+
+```bash
+# Run tests with Python 3.10 and Pydantic 2.10 (no coverage)
+python3 -m tox -e py310-pydantic210-nocov
+
+# Run tests with coverage
+python3 -m tox -e py310-pydantic210-cover
+
+# Run specific tests with tox
+python3 -m tox -e py310-pydantic210-nocov -- tests/test_vendor/test_catalog_v1.py
+```
+
+## Continuous Integration
+
+Tests run automatically on every push and pull request via GitHub Actions (`.github/workflows/github-actions.yml`).
+
+The CI runs tests across:
+- Python versions: 3.10, 3.11, 3.12, PyPy 3.10
+- Pydantic versions: 2.8, 2.10
+- With and without coverage reports

tests/conftest.py

@@ -3,6 +3,17 @@
 from pathlib import Path
 
 # Add src directory to Python path for all tests
+# This needs to run at import time, before pytest collects tests
 src_path = Path(__file__).parent.parent / "src"
 if str(src_path) not in sys.path:
     sys.path.insert(0, str(src_path))
+
+
+def pytest_configure(config):
+    """
+    Hook that runs before test collection.
+    Ensures src directory is in path before pytest imports test modules.
+    """
+    # Double-check src is in path
+    if str(src_path) not in sys.path:
+        sys.path.insert(0, str(src_path))