Add unit tests for Caesar cipher (#3665)

Co-authored-by: Yang Libin <contact@yanglibin.info>

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

@@ -0,0 +1,47 @@
+package com.thealgorithms.ciphers;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class CaesarTest {
+
+    Caesar caesar = new Caesar();
+
+    @Test
+    void caesarEncryptTest() {
+        // given
+        String textToEncrypt = "Encrypt this text";
+
+        // when
+        String cipherText = caesar.encode(textToEncrypt, 5);
+
+        // then
+        assertEquals("Jshwduy ymnx yjcy", cipherText);
+    }
+
+    @Test
+    void caesarDecryptTest() {
+        // given
+        String encryptedText = "Jshwduy ymnx yjcy";
+
+        // when
+        String cipherText = caesar.decode(encryptedText, 5);
+
+        // then
+        assertEquals("Encrypt this text", cipherText);
+    }
+
+    @Test
+    void caesarBruteForce() {
+        // given
+        String encryptedText = "Jshwduy ymnx yjcy";
+
+        // when
+        String[] allPossibleAnswers = caesar.bruteforce(encryptedText);
+
+        assertEquals(27, allPossibleAnswers.length);
+        assertEquals("Encrypt this text", allPossibleAnswers[5]);
+    }
+
+}