Add Polybius Cipher (#3185)

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

@@ -0,0 +1,45 @@
+package com.thealgorithms.ciphers;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class PolybiusTest {
+
+    @Test
+    void testEncrypt() {
+        // Given
+        String plaintext = "HELLOWORLD";
+
+        // When
+        String actual = Polybius.encrypt(plaintext);
+
+        // Then
+        assertEquals("12042121244124322103", actual);
+    }
+
+    @Test
+    void testDecrypt() {
+        // Given
+        String ciphertext = "12042121244124322103";
+
+        // When
+        String actual = Polybius.decrypt(ciphertext);
+
+        // Then
+        assertEquals("HELLOWORLD", actual);
+    }
+
+    @Test
+    void testIsTextTheSameAfterEncryptionAndDecryption() {
+        // Given
+        String plaintext = "HELLOWORLD";
+
+        // When
+        String encryptedText = Polybius.encrypt(plaintext);
+        String actual = Polybius.decrypt(encryptedText);
+
+        // Then
+        assertEquals(plaintext, actual);
+    }
+}