Add test case for CatalanNumber (#3698)

src/test/java/com/thealgorithms/dynamicprogramming/CatalanNumberTest.java

@@ -0,0 +1,14 @@
+package com.thealgorithms.dynamicprogramming;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+public class CatalanNumberTest {
+
+    @Test
+    public void testCatalanNumber() {
+        assertEquals(42, CatalanNumber.findNthCatalan(5));
+        assertEquals(16796, CatalanNumber.findNthCatalan(10));
+    }
+}