Fix Disabled Unit Tests in ReportServiceImplTest class

[pmoustopoulos]

Issue Description

The ReportServiceImplTest class in the src/test/java/com/ainigma100/departmentapi/service/impl/ directory has two disabled unit tests.

The first test, givenNoInput_whenGenerateAndZipReports_thenReturnFileDTO, is meant to verify that the method generates and zips reports correctly when there is data available. It sets up mock data and mock behavior for the dependencies and asserts that the resulting FileDTO object is not null and contains the expected file content. The verification is done using various verify statements to ensure that the dependencies are invoked with the expected arguments.

The second test, givenNoInput_whenGenerateAndZipReports_thenReturnFileDTOWithEmptyContent, is meant to verify the behavior when there is no data available for the reports. It sets up mock data and behavior to simulate an empty result from the repository and asserts that the resulting FileDTO object is not null but has a null file content. Similarly, the dependencies' invocations are verified using verify statements.