SOLR-10272: More detailed error message, explaining what to do

solr/core/src/test-files/solr/configsets/_default/conf/solrconfig.xml

@@ -24,7 +24,7 @@
   <luceneMatchVersion>${tests.luceneMatchVersion:LATEST}</luceneMatchVersion>
 
   <requestHandler name="my_error_handler" class="solr.ThrowErrorOnInitRequestHandler">
-    <str name="error">This is the _default configset, which is designed to throw error upon collection creation.</str>
+    <str name="error">This is the _default configset, which is designed to throw error upon collection creation from unit tests. If you see this error while running a unit test, you might want to explicitly specify the configset (when creating a collection) you intend to use (usually named "conf1" or "conf" etc.).</str>
   </requestHandler>
 
   <schemaFactory class="ClassicIndexSchemaFactory"/>

solr/core/src/test/org/apache/solr/cloud/CollectionsAPISolrJTest.java

@@ -71,7 +71,7 @@ public class CollectionsAPISolrJTest extends SolrCloudTestCase {
     System.out.println("Errors are: "+response.getErrorMessages());
     assertTrue(response.getErrorMessages() != null && response.getErrorMessages().size() > 0);
     assertTrue(response.getErrorMessages().getVal(0).contains("This is the _default configset, which is designed"
-        + " to throw error upon collection creation."));
+        + " to throw error upon collection creation"));
   }
 
   @Test