[YouTube] Test that no banner is returned for carouselHeaderRenders

Author: AudricV

extractor/src/test/java/org/schabi/newpipe/extractor/services/youtube/YoutubeChannelExtractorTest.java

@@ -2,6 +2,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
@@ -720,7 +721,8 @@ public void testAvatarUrl() throws Exception {
 
         @Test
         public void testBannerUrl() throws Exception {
-            // CarouselHeaderRender does not contain a banner
+            // CarouselHeaderRenders do not contain a banner
+            assertNull(extractor.getBannerUrl());
         }
 
         @Test