This commit is related to BAEL-7856 (#16480)

This commit aims to add a test class named "LastOccurrenceFinderUnitTest".

core-java-modules/core-java-string-operations-9/src/test/java/com/baeldung/LastOccurrenceFinder/LastOccurrenceFinderUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.LastOccurrenceFinder;
+
+import org.junit.Test;
+
+import java.util.OptionalInt;
+import java.util.stream.IntStream;
+
+import static org.junit.Assert.assertEquals;
+
+public class LastOccurrenceFinderUnitTest {
+    String str = "Welcome to Baeldung";
+    char target = 'e';
+    int n = 2;
+    int expectedIndex = 6;
+
+    @Test
+    public void givenStringAndCharAndN_whenFindingNthLastOccurrence_thenCorrectIndexReturned() {
+        int count = 0;
+        int index = -1;
+        for (int i = str.length() - 1; i >= 0; i--) {
+            if (str.charAt(i) == target) {
+                count++;
+                if (count == n) {
+                    index = i;
+                    break;
+                }
+            }
+        }
+        assertEquals(expectedIndex, index);
+    }
+
+    @Test
+    public void givenStringAndCharAndN_whenFindingNthLastOccurrenceUsingStreams_thenCorrectIndexReturned() {
+
+        OptionalInt result = IntStream.range(0, str.length())
+                .map(i -> str.length() - 1 - i)
+                .filter(i -> str.charAt(i) == target)
+                .skip(n - 1)
+                .findFirst();
+        int index = result.orElse(-1);
+        assertEquals(expectedIndex, index);
+    }
+}