Add comprehensive unit tests for >80% code coverage

[devin-ai-integration]

Add comprehensive unit tests for >80% code coverage

Summary

This PR expands unit test coverage for the Spring Boot banking application from a single context load test to 104 comprehensive tests across all layers. The tests cover models, services, controllers, repositories, and security configuration.

Changes:

• Added H2 in-memory database dependency for testing
• Created test configuration (application.properties) for H2 database
• Added model tests: AccountTest (9 tests), TransactionTest (10 tests)
• Added service tests: AccountServiceTest (20 tests) using Mockito
• Added controller tests: BankControllerTest (18 tests) using @WebMvcTest
• Added repository tests: AccountRepositoryTest (13 tests), TransactionRepositoryTest (18 tests) using @DataJpaTest
• Added security tests: SecurityConfigTest (15 tests)

All 104 tests pass locally.

Review & Testing Checklist for Human

• Verify actual coverage percentage - The tests pass locally but SonarQube in CI will measure actual coverage. Confirm it meets the >80% target when the pipeline runs.
• Review service layer test coverage - AccountServiceTest is the most critical; verify all business logic paths (deposit, withdraw, transfer, insufficient funds) are properly tested
• Check H2 vs MySQL compatibility - Tests use H2 in-memory database; verify no MySQL-specific features are missed in testing
• Validate security test mocking - SecurityConfigTest mocks AccountService; confirm this adequately tests authentication/authorization flows

Recommended test plan:

1. Wait for CI/SonarQube to report actual coverage metrics
2. If coverage is below 80%, identify uncovered lines and add additional tests
3. Optionally run the application locally and manually test a few flows to ensure tests align with actual behavior

Notes

• Tests are skipped during Docker builds (-DskipTests=true in Dockerfile) but run during SonarQube analysis stage
• Controller tests import SecurityConfig to properly test authentication redirects

Link to Devin run: https://app.devin.ai/sessions/2f20945dc8344d80a104a3b6fc0955f6
Requested by: Cindy Huang (@cindyyhuang)

[devin-ai-integration]

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