public void Exists_Should_ThrowException_IfArgumentIsNull()
 {
     Assert.Throws <ArgumentNullException>(() => _genericServiceNullable.Exists((int?)null));
 }
        public void Exists_Should_InvokeGenericRepositoryExits_Once()
        {
            var returnValue = _genericService.Exists(_testId);

            _mockGenericRepository.Verify(x => x.Exists(_testId), Times.Once);
        }