Refactored ReverseStringUsingStack

Author: navaneedan07

src/test/java/com/thealgorithms/strings/ReverseStringTest.java

@@ -1,7 +1,9 @@
 package com.thealgorithms.strings;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
+import org.junit.jupiter.api.Test;
 import java.util.stream.Stream;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
@@ -38,13 +40,8 @@ public void testReverseString4(String input, String expectedOutput) {
         assertEquals(expectedOutput, ReverseString.reverse4(input));
     }
 
-    @ParameterizedTest
-    @MethodSource("testCases")
-    public void testReverseString4WithNullInput(String input, String expectedOutput) {
-        if (input == null) {
-            assertThrows(IllegalArgumentException.class, () -> ReverseString.reverse4(input));
-        } else {
-            assertEquals(expectedOutput, ReverseString.reverse4(input));
-        }
+    @Test
+    public void testReverseString4WithNullInput() {
+        assertThrows(IllegalArgumentException.class, () -> ReverseString.reverse4(null));
     }
 }