- Add JUnit 5 and Mockito test dependencies to root pom.xml
- Add maven-surefire-plugin configuration for test execution
- Create BaseTest abstract class for Spring + Mockito support
- Add SysUserServiceImplTest with 7 test cases (CRUD operations, username uniqueness)
- Add AccountServiceImplTest with 5 test cases (CRUD operations)
- Add StringUtilsTest with 10 test cases (string utility methods)
- Total: 22 test cases, all passing