Add unit tests for FibonacciNumberCheck (#4225)

src/main/java/com/thealgorithms/maths/FibonacciNumberCheck.java

@@ -0,0 +1,35 @@
+package com.thealgorithms.maths;
+
+/**
+ * Fibonacci: 0 1 1 2 3 5 8 13 21 ...
+ * This code checks Fibonacci Numbers up to 45th number.
+ * Other checks fail because of 'long'-type overflow.
+ */
+public class FibonacciNumberCheck {
+    /**
+     * Check if a number is perfect square number
+     *
+     * @param number the number to be checked
+     * @return <tt>true</tt> if {@code number} is a perfect square, otherwise
+     *         <tt>false</tt>
+     */
+    public static boolean isPerfectSquare(long number) {
+        long sqrt = (long) Math.sqrt(number);
+        return sqrt * sqrt == number;
+    }
+
+    /**
+     * Check if a number is a Fibonacci number. This is true if and only if at
+     * least one of 5x^2+4 or 5x^2-4 is a perfect square
+     *
+     * @param number the number
+     * @return <tt>true</tt> if {@code number} is a Fibonacci number, otherwise
+     *         <tt>false</tt>
+     * @link https://en.wikipedia.org/wiki/Fibonacci_number#Identification
+     */
+    public static boolean isFibonacciNumber(long number) {
+        long value1 = 5 * number * number + 4;
+        long value2 = 5 * number * number - 4;
+        return isPerfectSquare(value1) || isPerfectSquare(value2);
+    }
+}