Testing a service that makes database calls, without a database
Something that stands out is that calling voMock.getFileName() on mocked instances will always return null as no mock response has been defined. So your validation logic of

assertThat(voResult.getFileName())
            .isEqualTo(voMock.getFileName());


essentially winds up being

assertThat(voResult.getFileName())
            .isEqualTo(null);


This could end up giving false positives where voResult is incorrect, but the test passes because the filename is null.

You would need to specify a filename for the response object by calling when(voMock.getFileName()).thenReturn("TestFile"). This way your test can actually determine that the returned object is the expected one by checking the unique expected value of voMock.getFileName().

Alternatively, if the requirement is that the instance returned from the service method is the same instance that the *Proc method returns, just avoid calling getFileName when you're verifying the test result. You could instead use something like assertSame(voMock, voResult) to ensure that the instance returned by the service method is the same one that is returned by the *Proc method.

I would always also recommend writing fail/error cases for your class as well. I couldn't give an example without seeing the FusServiceImpl class, but it can sometimes help with spotting issues like the one I listed above. For instance, if you have a test case like

@Test
public void whenGetFileById_thenReturnFile(){
    final Long ID = 99999L;

    when(getFileInfobyIdProc.get(ID)).thenReturn(voMock);



    FileInfoVO voResult = service.getFile(ID - 1);

    assertThat(voResult.getFileName())
            .isNotEqualTo(voMock.getFileName());


}


and that test case passes, you know you've probably made a mistake in the test logic. You can also validate that the method fails in the correct manner - does it return an object with null filename? A null return value? Or raise an exception? It's the non-ideal cases that will crash applications in production, so make sure to test for those cases as well.