Implement comprehensive test suite for Neo4j authentication improvements

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Description

Following the code review for PR #57 (Neo4j 5.x authentication compatibility), we need to implement a comprehensive test suite to validate the authentication improvements and ensure robustness.

Test Coverage Needed

Core Authentication Tests

• ✅ Neo4j 5.x authentication success scenarios with basic_auth()
• ✅ Neo4j 4.x fallback scenarios with tuple authentication
• ✅ Authentication failure handling and error messages
• ✅ Authentication verification functionality
• ✅ Connection retry behavior with exponential backoff

Security and Error Handling Tests

• ✅ Error message sanitization to prevent credential exposure
• ✅ Robust handling of various authentication error types
• ✅ Proper exception propagation and error recovery

Health Check and Diagnostics Tests

• ✅ Health check functionality with both read-only and write modes
• ✅ Server info retrieval and diagnostics
• ✅ Connection pooling and resource management

Integration Tests

• ✅ End-to-end authentication workflow testing
• ✅ Cross-version compatibility testing (Neo4j 4.x vs 5.x)
• ✅ Performance testing under various load conditions

Technical Requirements

Test Framework

• Use pytest for test organization and execution
• Mock Neo4j driver interactions for unit tests
• Use testcontainers or similar for integration tests with real Neo4j instances

Test Structure

tests/
├── unit/
│   ├── test_neo4j_manager_auth.py      # Authentication logic tests
│   ├── test_neo4j_manager_health.py    # Health check tests  
│   └── test_neo4j_manager_security.py  # Security and sanitization tests
├── integration/
│   ├── test_neo4j_compatibility.py     # Cross-version compatibility
│   └── test_neo4j_performance.py       # Performance and load tests
└── fixtures/
    ├── mock_responses.py               # Mock Neo4j responses
    └── test_data.py                    # Test data sets

Test Scenarios

1. Authentication Success Paths

   • Basic auth with Neo4j 5.x server
   • Tuple auth with Neo4j 4.x server
   • Authentication verification after connection

2. Authentication Failure Paths

   • Invalid credentials handling
   • "Missing key principal" error handling
   • Fallback mechanism activation
   • Multiple retry attempts with backoff

3. Security Validation

   • Error message sanitization effectiveness
   • No credential exposure in logs
   • Proper exception handling without information leakage

4. Health and Diagnostics

   • Health check with write operations enabled/disabled
   • Server info retrieval under various server states
   • Connection pooling behavior validation

Acceptance Criteria

• Test coverage of at least 90% for Neo4jManager class
• All authentication scenarios covered with unit tests
• Integration tests with both Neo4j 4.x and 5.x containers
• Security tests validating no credential exposure
• Performance benchmarks for connection establishment
• Comprehensive documentation of test scenarios

Implementation Notes

• Tests should be independent and can run in parallel
• Use environment variables for test configuration
• Include both positive and negative test cases
• Mock external dependencies appropriately
• Ensure tests are deterministic and reproducible

This test suite will provide confidence in the authentication improvements and serve as regression protection for future changes.

Generated following code review feedback for PR #57.