Add unit tests for Vigenere cipher (TheAlgorithms#3666)

src/main/java/com/thealgorithms/ciphers/Vigenere.java

@@ -8,10 +8,11 @@
  */
 public class Vigenere {
 
-    public static String encrypt(final String message, final String key) {
+    public String encrypt(final String message, final String key) {
         StringBuilder result = new StringBuilder();
 
-        for (int i = 0, j = 0; i < message.length(); i++) {
+        int j = 0;
+        for (int i = 0; i < message.length(); i++) {
             char c = message.charAt(i);
             if (Character.isLetter(c)) {
                 if (Character.isUpperCase(c)) {
@@ -39,10 +40,11 @@ public static String encrypt(final String message, final String key) {
         return result.toString();
     }
 
-    public static String decrypt(final String message, final String key) {
+    public String decrypt(final String message, final String key) {
         StringBuilder result = new StringBuilder();
 
-        for (int i = 0, j = 0; i < message.length(); i++) {
+        int j = 0;
+        for (int i = 0; i < message.length(); i++) {
             char c = message.charAt(i);
             if (Character.isLetter(c)) {
                 if (Character.isUpperCase(c)) {
@@ -66,13 +68,4 @@ public static String decrypt(final String message, final String key) {
         }
         return result.toString();
     }
-
-    public static void main(String[] args) {
-        String text = "Hello World!";
-        String key = "itsakey";
-        System.out.println(text);
-        String ciphertext = encrypt(text, key);
-        System.out.println(ciphertext);
-        System.out.println(decrypt(ciphertext, key));
-    }
 }

src/test/java/com/thealgorithms/ciphers/VigenereTest.java

@@ -0,0 +1,37 @@
+package com.thealgorithms.ciphers;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class VigenereTest {
+
+    Vigenere vigenere = new Vigenere();
+
+    @Test
+    void vigenereEncryptTest() {
+        // given
+        String text = "Hello World!";
+        String key = "suchsecret";
+
+        // when
+        String cipherText = vigenere.encrypt(text, key);
+
+        // then
+        assertEquals("Zynsg Yfvev!", cipherText);
+    }
+
+    @Test
+    void vigenereDecryptTest() {
+        // given
+        String encryptedText = "Zynsg Yfvev!";
+        String key = "suchsecret";
+
+        // when
+        String decryptedText = vigenere.decrypt(encryptedText, key);
+
+        // then
+        assertEquals("Hello World!", decryptedText);
+    }
+
+}