I’m using MediatR, and I’d like to test the logic inside the Handle method before saving the changes in the database. Here’s the code snippet:

  public async Task<int> Handle(CreateSubItemCommand command, CancellationToken cancellationToken)
    {
        var item = await _repository.FindByIdAsync(command.itemId, cancellationToken);
    
        if (item == null)
        {
            throw new ArgumentException($"The specified item was not found");
        }

     ItemModification(command, item);
     var subItemId = createSubItem(item,command)  
  _repository.Update(item);   
        await repository.UnitOfWork.SaveEntitiesAsync(cancellationToken).ConfigureAwait(false);
    
        return subItemId .Id;
    }

I created the unit test with moq

[Fact]
 public async void Test() {
   
     //Arrange
 var repository = new Mock<IRepository>();
 var command = new CreateSubItemCommand(....);

  var handler = new CreateSubItemCommandHandler(repository.Object);
     //Act var subItemId = await handler.Handle(command, new System.Threading.CancellationToken());
     //Assert 
    }

I don’t know how I can test the item before saving it to the database