Like I said, you have to add "facadeview.list+Control.IsVisible(1242)" in your visible part to your "New Serie Image" and you don't need the "this is a test" part. This is only for testing.
Code:
<!-- Neue Serien Image Anfang -->
<control>
<description>New Serie Image</description>
<posX>19</posX>
<posY>495</posY>
<type>image</type>
<id>0</id>
<width>100</width>
<height>100</height>
<texture>new_series.png</texture>
<visible>string.equals(#TVSeries.Series.HasNewEpisodes,1)+facadeview.list+Control.IsVisible(1242)</visible>
<!-- <colordiffuse>99FFFFFF</colordiffuse> -->
</control>
<control>
<type>label</type>
<description>Dummy Label for Series Posters</description>
<id>1242</id>
<posX>-50</posX>
<posY>-50</posY>
<label></label>
<visible>false</visible>
</control>
<!-- Neue Serien Image Ende -->