Add XOR Cipher (#5490)

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

@@ -0,0 +1,34 @@
+package com.thealgorithms.ciphers;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+class XORCipherTest {
+
+    @Test
+    void xorEncryptTest() {
+        // given
+        String plaintext = "My t&xt th@t will be ençrypted...";
+        String key = "My ç&cret key!";
+
+        // when
+        String cipherText = XORCipher.encrypt(plaintext, key);
+
+        // then
+        assertEquals("000000b7815e1752111c601f450e48211500a1c206061ca6d35212150d4429570eed", cipherText);
+    }
+
+    @Test
+    void xorDecryptTest() {
+        // given
+        String cipherText = "000000b7815e1752111c601f450e48211500a1c206061ca6d35212150d4429570eed";
+        String key = "My ç&cret key!";
+
+        // when
+        String plainText = XORCipher.decrypt(cipherText, key);
+
+        // then
+        assertEquals("My t&xt th@t will be ençrypted...", plainText);
+    }
+}