Add LongestValidParenthesesTest (#3612)

src/test/java/com/thealgorithms/dynamicprogramming/LongestValidParenthesesTest

@@ -0,0 +1,51 @@
+package com.thealgorithms.dynamicprogramming;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class LongestValidParenthesesTest {
+
+    LongestValidParentheses longestValidParentheses = new LongestValidParentheses();
+
+    @Test
+    void shouldReturnZeroWhenSingleOpeningParenthesisIsGiven() {
+        String input = "(";
+        int validLength = longestValidParentheses.getLongestValidParentheses(input);
+        assertEquals(0, validLength);
+    }
+
+    @Test
+    void shouldReturnZeroWhenSingleClosingParenthesisIsGiven() {
+        String input = ")";
+        int validLength = longestValidParentheses.getLongestValidParentheses(input);
+        assertEquals(0, validLength);
+    }
+
+    @Test
+    void shouldReturnZeroWhenNullStringIsGiven() {
+        String input = "";
+        int validLength = longestValidParentheses.getLongestValidParentheses(input);
+        assertEquals(0, validLength);
+    }
+
+    @Test
+    void shouldReturnTwoWhenTwoBalancedParenthesesAreGiven() {
+        String input = "()";
+        int validLength = longestValidParentheses.getLongestValidParentheses(input);
+        assertEquals(2, validLength);
+    }
+
+    @Test
+    void shouldReturnLengthWhenInputStringIsValid() {
+        String input = "()((()))";
+        int validLength = longestValidParentheses.getLongestValidParentheses(input);
+        assertEquals(8, validLength);
+    }
+
+    @Test
+    void shouldReturnValidLengthWhenInputStringIsGiven() {
+        String input = "((()((())))";
+        int validLength = longestValidParentheses.getLongestValidParentheses(input);
+        assertEquals(10, validLength);
+    }
+}