Invoking EventCallback on mocked child component does not update field on parent

[EHartfelt]

Hi
I have a test where I'm mocking a razor component on a page.
The component has an EventCallback that updates a private field on the parent page.
This works fine when running the application.
However, I can't get it to work in the test. In the test, I create a mock of the child component and then invoke the callback on the mock. This doesn't seem to update the field on the parent.

Here is minimal example

"Parent.razor"

@page "/"

<PageTitle>Home</PageTitle>

<ChildComponent @ref="m_childComponent" OnUpdate="newValue => m_value = newValue"/>

<h2>Value is: @m_value</h2>

"Parent.razor.cs"

public partial class Parent
{
    private int m_value = 1;
    private ChildComponent m_childComponent;
}

"ChildComponent.razor"

<h3>ChildComponent</h3>

@code {}

"ChildComponent.razor.cs"

public partial class ChildComponent : ComponentBase
{
    [Parameter]
    public EventCallback<int> OnUpdate { get; set; }

    protected override async Task OnInitializedAsync()
    {
        await OnUpdate.InvokeAsync(42);
    }
}

"Test.cs"

[TestClass]
public class ExampleTest : Bunit.TestContext
{
    [TestMethod]
    public async Task Update_Value_On_Parent_By_Invoking_Callback()
    {
        // ARRANGE
        var childComponentMock = new Mock<ChildComponent>();
        
        ComponentFactories.Add(childComponentMock.Object);
        var newValue = 100;
        
        // ACT
        var cut = RenderComponent<Parent>();
        await childComponentMock.Object.OnUpdate.InvokeAsync(newValue);
    
        // ASSERT
        cut.Find("h2").MarkupMatches($"<h2>Value is: {newValue}</h2>");
    }
}

The test fails with the following output

Actual HTML: 
<h2>Value is: 1</h2>

Expected HTML: 
<h2>Value is: 100</h2>

I found this issue #1186 which describes a similar approach, but it uses ComponentFactories.AddStub<T>(); instead of ComponentFactories.Add(someObject);, which I need.

Can you help me?