public class YourUserControl : UserControl
{
    // Note: DependencyProperty should always have the name (Property name) + "Property" suffix:
    // (Test -> TestProperty, Value -> ValueProperty...
    public static readonly DependencyProperty TestProperty = DependencyProperty.Register(nameof(Test), typeof(YourUserControl), typeof(int));

    // Here's your current property you bind to in Xaml: Test = {Binding ViewModel.TestValue}
    public int Test
    {
        get => (int)GetValue(TestProperty );
        set => SetValue(TestProperty, value);
    }
}