Add tests, remove main in PalindromePrime

Author: Hardvan

src/main/java/com/thealgorithms/misc/PalindromePrime.java

@@ -1,51 +1,49 @@
 package com.thealgorithms.misc;
 
-import java.util.Scanner;
+import java.util.ArrayList;
+import java.util.List;
 
 public final class PalindromePrime {
     private PalindromePrime() {
     }
 
-    public static void main(String[] args) { // Main function
-        Scanner in = new Scanner(System.in);
-        System.out.println("Enter the quantity of First Palindromic Primes you want");
-        int n = in.nextInt(); // Input of how many first palindromic prime we want
-        functioning(n); // calling function - functioning
-        in.close();
-    }
+    public static boolean prime(int num) {
+        if (num < 2) return false; // Handle edge case for numbers < 2
+        if (num == 2) return true; // 2 is prime
+        if (num % 2 == 0) return false; // Even numbers > 2 are not prime
 
-    public static boolean prime(int num) { // checking if number is prime or not
         for (int divisor = 3; divisor <= Math.sqrt(num); divisor += 2) {
             if (num % divisor == 0) {
-                return false; //  false if not prime
+                return false;
             }
         }
-        return true; // True if prime
+        return true;
     }
 
-    public static int reverse(int n) { //  Returns  the reverse of the number
+    public static int reverse(int n) {
         int reverse = 0;
         while (n != 0) {
-            reverse *= 10;
-            reverse += n % 10;
+            reverse = reverse * 10 + (n % 10);
             n /= 10;
         }
         return reverse;
     }
 
-    public static void functioning(int y) {
-        if (y == 0) {
-            return;
-        }
-        System.out.print(2 + "\n"); // print the first Palindromic Prime
+    public static List<Integer> generatePalindromePrimes(int n) {
+        List<Integer> palindromicPrimes = new ArrayList<>();
+        if (n <= 0) return palindromicPrimes; // Handle case for 0 or negative input
+
+        palindromicPrimes.add(2); // 2 is the first palindromic prime
         int count = 1;
         int num = 3;
-        while (count < y) {
-            if (num == reverse(num) && prime(num)) { // number is prime and it's reverse is same
-                count++; // counts check when to terminate while loop
-                System.out.print(num + "\n"); // print the Palindromic Prime
+
+        while (count < n) {
+            if (num == reverse(num) && prime(num)) {
+                palindromicPrimes.add(num);
+                count++;
             }
-            num += 2; // inrease iterator value by two
+            num += 2; // Skip even numbers
         }
+        return palindromicPrimes;
     }
 }

src/test/java/com/thealgorithms/misc/PalindromePrimeTest.java

@@ -0,0 +1,50 @@
+package com.thealgorithms.misc;
+
+import static org.junit.jupiter.api.Assertions.*;
+import org.junit.jupiter.api.Test;
+import java.util.List;
+
+public class PalindromePrimeTest {
+
+    @Test
+    public void testPrimeWithPrimeNumbers() {
+        assertTrue(PalindromePrime.prime(2), "2 should be prime");
+        assertTrue(PalindromePrime.prime(3), "3 should be prime");
+        assertTrue(PalindromePrime.prime(5), "5 should be prime");
+        assertTrue(PalindromePrime.prime(11), "11 should be prime");
+    }
+
+    @Test
+    public void testPrimeWithNonPrimeNumbers() {
+        assertFalse(PalindromePrime.prime(1), "1 is not prime");
+        assertFalse(PalindromePrime.prime(4), "4 is not prime");
+        assertFalse(PalindromePrime.prime(9), "9 is not prime");
+        assertFalse(PalindromePrime.prime(15), "15 is not prime");
+    }
+
+    @Test
+    public void testReverse() {
+        assertEquals(123, PalindromePrime.reverse(321), "Reverse of 321 should be 123");
+        assertEquals(7, PalindromePrime.reverse(7), "Reverse of 7 should be 7");
+        assertEquals(1221, PalindromePrime.reverse(1221), "Reverse of 1221 should be 1221");
+    }
+
+    @Test
+    public void testGeneratePalindromePrimes() {
+        List<Integer> result = PalindromePrime.generatePalindromePrimes(5);
+        List<Integer> expected = List.of(2, 3, 5, 7, 11);
+        assertEquals(expected, result, "The first 5 palindromic primes should be [2, 3, 5, 7, 11]");
+    }
+
+    @Test
+    public void testGeneratePalindromePrimesWithZero() {
+        List<Integer> result = PalindromePrime.generatePalindromePrimes(0);
+        assertTrue(result.isEmpty(), "Generating 0 palindromic primes should return an empty list");
+    }
+
+    @Test
+    public void testGeneratePalindromePrimesWithNegativeInput() {
+        List<Integer> result = PalindromePrime.generatePalindromePrimes(-5);
+        assertTrue(result.isEmpty(), "Generating a negative number of palindromic primes should return an empty list");
+    }
+}