Add cipher class, cipher tests, enhance docs in 'AtbashCipher.java' (#5690)

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

@@ -0,0 +1,28 @@
+package com.thealgorithms.ciphers;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class AtbashTest {
+
+    @Test
+    public void atbashEncrypt() {
+        AtbashCipher normalToEncrypt = new AtbashCipher("Hello World! 123, @cipher abcDEF ZYX 987 madam zzZ Palindrome!");
+        String expectedText = "Svool Dliow! 123, @xrksvi zyxWVU ABC 987 nzwzn aaA Kzormwilnv!";
+
+        normalToEncrypt.setString(normalToEncrypt.convert());
+
+        assertEquals(expectedText, normalToEncrypt.getString());
+    }
+
+    @Test
+    public void atbashDecrypt() {
+        AtbashCipher encryptToNormal = new AtbashCipher("Svool Dliow! 123, @xrksvi zyxWVU ABC 987 nzwzn aaA Kzormwilnv!");
+        String expectedText = "Hello World! 123, @cipher abcDEF ZYX 987 madam zzZ Palindrome!";
+
+        encryptToNormal.setString(encryptToNormal.convert());
+
+        assertEquals(expectedText, encryptToNormal.getString());
+    }
+}