Add unit tests for Caesar cipher (#3665)

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

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

@@ -1,7 +1,5 @@
 package com.thealgorithms.ciphers;
 
-import java.util.Scanner;
-
 /**
  * A Java implementation of Caesar Cipher. /It is a type of substitution cipher
  * in which each letter in the plaintext is replaced by a letter some fixed
@@ -18,7 +16,7 @@ public class Caesar {
      *
      * @return Encrypted message
      */
-    public static String encode(String message, int shift) {
+    public String encode(String message, int shift) {
         StringBuilder encoded = new StringBuilder();
 
         shift %= 26;
@@ -29,10 +27,10 @@ public class Caesar {
             // is in-order latin alphabet
             char current = message.charAt(i); // Java law : char + int = char
 
-            if (IsCapitalLatinLetter(current)) {
+            if (isCapitalLatinLetter(current)) {
                 current += shift;
                 encoded.append((char) (current > 'Z' ? current - 26 : current)); // 26 = number of latin letters
-            } else if (IsSmallLatinLetter(current)) {
+            } else if (isSmallLatinLetter(current)) {
                 current += shift;
                 encoded.append((char) (current > 'z' ? current - 26 : current)); // 26 = number of latin letters
             } else {
@@ -48,7 +46,7 @@ public class Caesar {
      *
      * @return message
      */
-    public static String decode(String encryptedMessage, int shift) {
+    public String decode(String encryptedMessage, int shift) {
         StringBuilder decoded = new StringBuilder();
 
         shift %= 26;
@@ -56,10 +54,10 @@ public class Caesar {
         final int length = encryptedMessage.length();
         for (int i = 0; i < length; i++) {
             char current = encryptedMessage.charAt(i);
-            if (IsCapitalLatinLetter(current)) {
+            if (isCapitalLatinLetter(current)) {
                 current -= shift;
                 decoded.append((char) (current < 'A' ? current + 26 : current)); // 26 = number of latin letters
-            } else if (IsSmallLatinLetter(current)) {
+            } else if (isSmallLatinLetter(current)) {
                 current -= shift;
                 decoded.append((char) (current < 'a' ? current + 26 : current)); // 26 = number of latin letters
             } else {
@@ -72,21 +70,21 @@ public class Caesar {
     /**
      * @return true if character is capital Latin letter or false for others
      */
-    private static boolean IsCapitalLatinLetter(char c) {
+    private static boolean isCapitalLatinLetter(char c) {
         return c >= 'A' && c <= 'Z';
     }
 
     /**
      * @return true if character is small Latin letter or false for others
      */
-    private static boolean IsSmallLatinLetter(char c) {
+    private static boolean isSmallLatinLetter(char c) {
         return c >= 'a' && c <= 'z';
     }
 
     /**
      *  @return string array which contains all the possible decoded combination.
      */
-    public static String[] bruteforce(String encryptedMessage) {
+    public String[] bruteforce(String encryptedMessage) {
         String[] listOfAllTheAnswers = new String[27];
         for (int i = 0; i <= 26; i++) {
             listOfAllTheAnswers[i] = decode(encryptedMessage, i);
@@ -94,47 +92,4 @@ public class Caesar {
 
         return listOfAllTheAnswers;
     }
-
-    public static void main(String[] args) {
-        Scanner input = new Scanner(System.in);
-        int shift = 0;
-        System.out.println("Please enter the message (Latin Alphabet)");
-        String message = input.nextLine();
-        System.out.println(message);
-        System.out.println("(E)ncode or (D)ecode or (B)ruteforce?");
-        char choice = input.next().charAt(0);
-        switch (choice) {
-            case 'E':
-            case 'e':
-                System.out.println("Please enter the shift number");
-                shift = input.nextInt() % 26;
-                System.out.println(
-                    "ENCODED MESSAGE IS \n" + encode(message, shift)
-                ); // send our function to handle
-                break;
-            case 'D':
-            case 'd':
-                System.out.println("Please enter the shift number");
-                shift = input.nextInt() % 26;
-                System.out.println(
-                    "DECODED MESSAGE IS \n" + decode(message, shift)
-                );
-                break;
-            case 'B':
-            case 'b':
-                String[] listOfAllTheAnswers = bruteforce(message);
-                for (int i = 0; i <= 26; i++) {
-                    System.out.println(
-                        "FOR SHIFT " +
-                        String.valueOf(i) +
-                        " decoded message is " +
-                        listOfAllTheAnswers[i]
-                    );
-                }
-            default:
-                System.out.println("default case");
-        }
-
-        input.close();
-    }
 }

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]);
+    }
+
+}