How to generate Concurrency exceptions in Entity Framework?

Question

Switching from a mono webserver to a webfarm, I need to re-implement a business critical feature to make it compatible with the webfarm. The code used to be something like:

private static readonly Object lockToken = new Object();
public void ChangeState(Foo bar)
{
    lock (lockToken)
    {
        // Change state logic
        
        /*
         *Some code
         */

        Context.Entities.SaveChanges();
    }
}

I know I can't keep the lock and must switch to application-managed concurrency tokens. Before doing that, and to make sure the implementation is correct I'd like to break my own code and make it throw reals DbUpdateConcurrencyException (ie: I want it to be thrown by the framework, not from my code). I tried using this code:

Parallel.For(0, 100, y =>
{
    Parallel.ForEach(objects, x =>
    {
        try
        {
            service.ChangeState(new Foo(x));
        }
        catch (DbUpdateConcurrencyException duce)
        {
            count++;
            LogManager.Log.Error("Concurrency Error", duce);
        }
    });
});

But I can't make it to happen.

The project is in .NET 4.8 / EF 6 / SQL Server 2016