When the sidebar is displayed normally, this is what contains all the widgets within it:
<div id="ipsLayout_sidebar" class="ipsLayout_sidebarright " data-controller="core.front.widgets.sidebar">
<div class="cWidgetContainer " data-controller="core.front.widgets.area" data-role="widgetReceiver" data-orientation="vertical" data-widgetarea="sidebar">
<ul class="ipsList_reset">
[EACH WIDGET THEN HAS ITS OWN <li></li>]
</ul>
</div>
</div>
When the advertisement is set to be shown in the sidebar is used, the ad is displayed in the sidebar as follows:
<div data-role="sidebarAd">TEST</div>
<br>
<br>
<div id="ipsLayout_sidebar" class="ipsLayout_sidebarright " data-controller="core.front.widgets.sidebar">
<div class="cWidgetContainer " data-controller="core.front.widgets.area" data-role="widgetReceiver" data-orientation="vertical" data-widgetarea="sidebar">
<ul class="ipsList_reset">
[EACH WIDGET THEN HAS ITS OWN <li></li>]
</ul>
</div>
</div>
And then when there are no widgets and the advertisment setting to force sidebar is used, you just get this:
<div data-role="sidebarAd">TEST</div>
<br>
<br>
If you really are not going to have any widgets displayed, then maybe make this the code for the advertisment instead:
<div id="ipsLayout_sidebar" class="ipsLayout_sidebarright">TEST</div>