How can I show in image using Slate?

I am working learning Slate for doing the UI. I am having a problem setting a background image. The background is all black and I do not see the image anywhere. What am I doing wrong? I have done searching the internet and the engine code and this seems to be how things should be done but I must be missing something.

Here is my code:

TSharedPtr<FSlateStyleSet> Style = MakeShareable(new FSlateStyleSet("ZombieHorde"));
    Style->SetContentRoot(FPaths::ProjectContentDir());
    Style->Set(
        FName("test"),
        new FSlateImageBrush(Style->RootToContentDir(TEXT("test"), TEXT(".png")),
        FVector2D(300.0, 300.0),
        FLinearColor(0,0,0,1))
    );
    
    ChildSlot
    [
        SNew(SOverlay) + SOverlay::Slot()
            .VAlign(VAlign_Fill)
            .HAlign(HAlign_Fill)
            [
                SNew(SImage)
                    .Image(Style->GetBrush(FName("test")))
            ]
    ....