tests: add GenericRootTest

Author: vil02

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

@@ -15,7 +15,7 @@ public static void main(String[] args) {
         System.out.println("Generic root of " + number2 + " is: " + result2);
     }
 
-    private static int genericRoot(int n) {
+    public static int genericRoot(int n) {
         int root = 0;
         while (n > 0 || root > 9) {
             if (n == 0) {

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

@@ -0,0 +1,17 @@
+package com.thealgorithms.maths;
+
+import static java.util.Map.entry;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Map;
+import org.junit.jupiter.api.Test;
+
+public class GenericRootTest {
+    @Test
+    public void testGenericRoot() {
+        final Map<Integer, Integer> testCases = Map.ofEntries(entry(0, 0), entry(1, 1), entry(12345, 6), entry(123, 6), entry(15937, 7), entry(222222, 3), entry(99999, 9));
+        for (final var tc : testCases.entrySet()) {
+            assertEquals(tc.getValue(), GenericRoot.genericRoot(tc.getKey()));
+        }
+    }
+}