How can I test return await _propertyRepository.UnitOfWork.SaveEntitiesAsync();?

AddCommandHandler

public async Task<bool> Handle(AddCommand message, CancellationToken cancellationToken)
{

    _logger.LogInformation("----- Adding Property - Property: {@Property}", property);

    _propertyRepository.Add(property);

    return await _propertyRepository.UnitOfWork.SaveEntitiesAsync();
}

Anyone please guide me to write test case for that only. I am writing like this. But the test case fails.

PropertyRepository

public class PropertyRepository : IPropertyRepository
    {
        private readonly RealxContext _realxContext;

        public IUnitOfWork UnitOfWork
        {
            get
            {
                return _realxContext;
            }
        }

        public PropertyRepository(RealxContext realxContext)
        {
            _realxContext = realxContext ?? throw new ArgumentNullException(nameof(realxContext));

        }

AddCommandHandlerTests.cs

_propertyRepository.Setup(propertyRepo => propertyRepo.UnitOfWork.SaveEntitiesAsync(default(CancellationToken))).Returns(Task.FromResult(true));