Update

src/main/java/ru/ilug/c6_word_group/WordGroupImpl.java

@@ -11,7 +11,6 @@ public class WordGroupImpl implements WordGroup {
     public Map<Integer, List<String>> groupWordsByLength(String text) {
         text = text.replaceAll("[.,]", "");
         return Arrays.stream(text.split(" "))
-                .map(String::toLowerCase)
                 .collect(Collectors.groupingBy(String::length));
     }
 }