Add Junit tests for ColumnarTranspositionCipher.java (#5599)

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

@@ -0,0 +1,47 @@
+package com.thealgorithms.ciphers;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class ColumnarTranspositionCipherTest {
+    private String keyword;
+    private String plaintext;
+
+    @BeforeEach
+    public void setUp() {
+        keyword = "keyword";
+        plaintext = "This is a test message for Columnar Transposition Cipher";
+    }
+
+    @Test
+    public void testEncryption() {
+        String encryptedText = ColumnarTranspositionCipher.encrpyter(plaintext, keyword);
+        assertNotNull(encryptedText, "The encrypted text should not be null.");
+        assertFalse(encryptedText.isEmpty(), "The encrypted text should not be empty.");
+        // Check if the encrypted text is different from the plaintext
+        assertNotEquals(plaintext, encryptedText, "The encrypted text should be different from the plaintext.");
+    }
+
+    @Test
+    public void testDecryption() {
+        String encryptedText = ColumnarTranspositionCipher.encrpyter(plaintext, keyword);
+        String decryptedText = ColumnarTranspositionCipher.decrypter();
+
+        assertEquals(plaintext.replaceAll(" ", ""), decryptedText.replaceAll(" ", ""), "The decrypted text should match the original plaintext, ignoring spaces.");
+        assertEquals(encryptedText, ColumnarTranspositionCipher.encrpyter(plaintext, keyword), "The encrypted text should be the same when encrypted again.");
+    }
+
+    @Test
+    public void testLongPlainText() {
+        String longText = "This is a significantly longer piece of text to test the encryption and decryption capabilities of the Columnar Transposition Cipher. It should handle long strings gracefully.";
+        String encryptedText = ColumnarTranspositionCipher.encrpyter(longText, keyword);
+        String decryptedText = ColumnarTranspositionCipher.decrypter();
+        assertEquals(longText.replaceAll(" ", ""), decryptedText.replaceAll(" ", ""), "The decrypted text should match the original long plaintext, ignoring spaces.");
+        assertEquals(encryptedText, ColumnarTranspositionCipher.encrpyter(longText, keyword), "The encrypted text should be the same when encrypted again.");
+    }
+}