adding the fibonacci series to the Recursion package

src/main/java/com/thealgorithms/Recursion/FibonacciSeries.java

@@ -0,0 +1,21 @@
+package com.thealgorithms.Recursion;
+
+/*
+    The Fibonacci series is a sequence of numbers where each number is the sum of the two preceding ones,
+    starting with 0 and 1.
+       NUMBER    0 1 2 3 4 5 6 7  8  9  10 ...
+       FIBONACCI 0 1 1 2 3 5 8 13 21 34 55 ...
+*/
+
+public final class FibonacciSeries {
+    private FibonacciSeries() {
+        throw new UnsupportedOperationException("Utility class");
+    }
+    public static int fibonacci(int n) {
+        if (n <= 1) {
+            return n;
+        } else {
+            return fibonacci(n - 1) + fibonacci(n - 2);
+        }
+    }
+}

src/test/java/com/thealgorithms/Recursion/FibonacciSeriesTest.java

@@ -0,0 +1,27 @@
+package com.thealgorithms.Recursion;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class FibonacciSeriesTest {
+
+    @Test
+    public void testFibonacci() {
+        assertEquals(0, FibonacciSeries.fibonacci(0));
+        assertEquals(1, FibonacciSeries.fibonacci(1));
+        assertEquals(1, FibonacciSeries.fibonacci(2));
+        assertEquals(2, FibonacciSeries.fibonacci(3));
+        assertEquals(3, FibonacciSeries.fibonacci(4));
+        assertEquals(5, FibonacciSeries.fibonacci(5));
+        assertEquals(8, FibonacciSeries.fibonacci(6));
+        assertEquals(13, FibonacciSeries.fibonacci(7));
+        assertEquals(21, FibonacciSeries.fibonacci(8));
+        assertEquals(34, FibonacciSeries.fibonacci(9));
+        assertEquals(55, FibonacciSeries.fibonacci(10));
+        assertEquals(89, FibonacciSeries.fibonacci(11));
+        assertEquals(144, FibonacciSeries.fibonacci(12));
+        assertEquals(233, FibonacciSeries.fibonacci(13));
+        assertEquals(377, FibonacciSeries.fibonacci(14));
+    }
+}