Add Catalan number (#5846)

src/test/java/com/thealgorithms/maths/CatalanNumbersTest.java

@@ -0,0 +1,43 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+
+/**
+ * Test class for CatalanNumbers
+ */
+class CatalanNumbersTest {
+
+    /**
+     * Provides test data for the parameterized Catalan number test.
+     * Each array contains two elements:
+     * [input number, expected Catalan number for that input]
+     */
+    static Stream<Object[]> catalanNumbersProvider() {
+        return Stream.of(new Object[] {0, 1}, new Object[] {1, 1}, new Object[] {2, 2}, new Object[] {3, 5}, new Object[] {4, 14}, new Object[] {5, 42}, new Object[] {6, 132}, new Object[] {7, 429}, new Object[] {8, 1430}, new Object[] {9, 4862}, new Object[] {10, 16796});
+    }
+
+    /**
+     * Parameterized test for checking the correctness of Catalan numbers.
+     * Uses the data from the provider method 'catalanNumbersProvider'.
+     */
+    @ParameterizedTest
+    @MethodSource("catalanNumbersProvider")
+    void testCatalanNumbers(int input, int expected) {
+        assertEquals(expected, CatalanNumbers.catalan(input), () -> String.format("Catalan number for input %d should be %d", input, expected));
+    }
+
+    /**
+     * Test for invalid inputs which should throw an IllegalArgumentException.
+     */
+    @Test
+    void testIllegalInput() {
+        assertThrows(IllegalArgumentException.class, () -> CatalanNumbers.catalan(-1));
+        assertThrows(IllegalArgumentException.class, () -> CatalanNumbers.catalan(-5));
+    }
+}