Creating mock of method that receive parameter of other method and change attribute, using Moq and Xunit

Question

protected virtual TMyClass GetMockMyClass<TMyClass>(Action<Mock<TMyClass>> setup = null) where TMyClass : class
{
    var mockMyClass = new Mock<TMyClass>();
    setup?.Invoke(mockMyClass);
    return mockMyClass.Object;
}

I need to test this method:

public async Task<FirstDto> FirstAsync(string argument)
{
    var result = await this.InternalMethod(argument);

    await this.CreateAsync(new Second()
    {
        // I haven't Id!!!!
        Error = result.error,
        Argument = argument,
        State = result.Success,
    });

    return result;
}

Here we go!

var myMockMyClass = GetMockMyClass<IMyClass<SecondDto, Second>>(mock =>
{
    mock.Setup(x => x.CreateAsync(It.IsAny<Second>()))
        .ReturnsAsync(this.mapper.Map<SecondDto>(

                    /* Set manually the Id (or other attribute) in test SCOPE? */

                    ));
});

await myMockMyClass.FirstAsync("someValue");

// now I need to check that a new register or Second object class...

var entityWithError = await myRepo
                    .Search<Second>(x => !string.IsNullOrEmpty(x.Error))
                    .FirstOrDefaultAsync();

In my mock I need to set previously the value of the Id in order to prevent

System.NotSupportedException : The property 'Second.Id' does not have a value set and no value generator is available for properties of type 'decimal'. Either set a value for the property before adding the entity or configure a value generator for properties of type 'decimal' in 'OnModelCreating'.

How set the ID in the mock?