Added new tests for the main Levenshtein algorithm implementation classes

Author: TheRealHaui

src/test/java/org/apache/commons/text/similarity/LevenshteinDetailedDistanceTest.java

@@ -41,6 +41,10 @@ void testApplyThrowsIllegalArgumentExceptionAndCreatesLevenshteinDetailedDistanc
     void testApplyWithNullSimilarityInput() {
         assertThrows(IllegalArgumentException.class,
                 () -> new LevenshteinDetailedDistance(0).apply((SimilarityInput<Object>) null, (SimilarityInput<Object>) null));
+        assertThrows(IllegalArgumentException.class,
+                () -> new LevenshteinDetailedDistance(0).apply(new SimilarityCharacterInput("asdf"), (SimilarityCharacterInput) null));
+        assertThrows(IllegalArgumentException.class,
+                () -> new LevenshteinDetailedDistance(0).apply((SimilarityCharacterInput) null, new SimilarityCharacterInput("asdf")));
     }
 
     @Test

src/test/java/org/apache/commons/text/similarity/LevenshteinDistanceTest.java

@@ -34,6 +34,10 @@ class LevenshteinDistanceTest {
     @Test
     void testApplyThrowsIllegalArgumentExceptionSimilarityInput() {
         assertThrows(IllegalArgumentException.class, () -> new LevenshteinDistance(0).apply((SimilarityInput<Object>) null, (SimilarityInput<Object>) null));
+        assertThrows(IllegalArgumentException.class, () -> new LevenshteinDistance(0).apply(new SimilarityCharacterInput("asdf"),
+                (SimilarityCharacterInput) null));
+        assertThrows(IllegalArgumentException.class, () -> new LevenshteinDistance(0).apply((SimilarityCharacterInput) null,
+                new SimilarityCharacterInput("asdf")));
     }
 
     @Test