docs: update README and add test infrastructure

- Enhance .gitignore with comprehensive Python patterns
- Improve README with better setup and testing instructions
- Add test infrastructure:
  * Test requirements file
  * Environment setup script
  * Test runner script
  * Comprehensive test suite
  * Coverage configuration

tests/README.md

@@ -0,0 +1,92 @@
+# Testing
+
+This directory contains tests for the OIDC validator application.
+
+## Setup
+
+### Using the setup script (recommended)
+
+1. Run the setup script:
+   ```bash
+   ./setup_test_env.sh
+   ```
+
+This will create a virtual environment and install all dependencies.
+
+### Manual setup
+
+1. Create and activate a virtual environment:
+   ```bash
+   python3 -m venv venv
+   source venv/bin/activate
+   ```
+
+2. Install application dependencies:
+   ```bash
+   pip install -r requirements.txt
+   ```
+
+3. Install test dependencies:
+   ```bash
+   pip install -r requirements-test.txt
+   ```
+
+## Running Tests
+
+### Using the test runner script (recommended)
+
+```bash
+./run_tests.sh
+```
+
+This will automatically activate the virtual environment and run the tests.
+
+### Manual execution
+
+1. Activate the virtual environment:
+   ```bash
+   source venv/bin/activate
+   ```
+
+2. Run tests:
+   ```bash
+   # Run all tests
+   pytest
+   
+   # Run tests with coverage (excluding tests directory)
+   pytest --cov=. --cov-config=.coveragerc
+   
+   # Run tests with verbose output
+   pytest -v
+   ```
+
+3. Deactivate the virtual environment when done:
+   ```bash
+   deactivate
+   ```
+
+## Coverage Reports
+
+The test suite generates coverage reports to help you understand how well the code is tested:
+
+- Terminal coverage report is displayed after running tests
+- HTML coverage report is generated in the `htmlcov/` directory
+- The coverage configuration excludes the tests directory itself from coverage statistics
+
+## Test Structure
+
+- `conftest.py`: Contains pytest fixtures shared across tests
+- `test_main.py`: Tests for the main FastAPI application endpoints
+- `test_token_validation.py`: Tests for token validation and refresh logic
+- `test_utils.py`: Tests for utility functions
+
+## Test Coverage
+
+The tests cover:
+- Health check endpoint
+- Token validation endpoint
+- Token refresh endpoint
+- Client configuration endpoint
+- Utility functions for OIDC operations
+- Error handling for various failure scenarios
+- Edge cases and invalid inputs