Add test cases for TrappingRainwater algorithm

Author: Arzoo1701

src/test/java/com/thealgorithms/searches/TrappingRainwaterTest.java

@@ -1,6 +1,7 @@
 package com.thealgorithms.searches;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+
 import org.junit.jupiter.api.Test;
 
 public class TrappingRainwaterTest {