refactor: OnesComplement Tests Using Parameterized Inputs (#6375)

refactor: OnesComplement Tests Using Parameterized Inputs

Co-authored-by: Deniz Altunkapan <93663085+DenizAltunkapan@users.noreply.github.com>

src/main/java/com/thealgorithms/bitmanipulation/OnesComplement.java

@@ -12,15 +12,24 @@ public final class OnesComplement {
     private OnesComplement() {
     }
 
-    // Function to get the 1's complement of a binary number
+    /**
+     * Returns the 1's complement of a binary string.
+     *
+     * @param binary A string representing a binary number (e.g., "1010").
+     * @return A string representing the 1's complement.
+     * @throws IllegalArgumentException if the input is null or contains characters other than '0' or '1'.
+     */
     public static String onesComplement(String binary) {
-        StringBuilder complement = new StringBuilder();
-        // Invert each bit to get the 1's complement
-        for (int i = 0; i < binary.length(); i++) {
-            if (binary.charAt(i) == '0') {
-                complement.append('1');
-            } else {
-                complement.append('0');
+        if (binary == null || binary.isEmpty()) {
+            throw new IllegalArgumentException("Input must be a non-empty binary string.");
+        }
+
+        StringBuilder complement = new StringBuilder(binary.length());
+        for (char bit : binary.toCharArray()) {
+            switch (bit) {
+                case '0' -> complement.append('1');
+                case '1' -> complement.append('0');
+                default -> throw new IllegalArgumentException("Input must contain only '0' and '1'. Found: " + bit);
             }
         }
         return complement.toString();

src/test/java/com/thealgorithms/bitmanipulation/OnesComplementTest.java

@@ -1,8 +1,12 @@
 package com.thealgorithms.bitmanipulation;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.NullAndEmptySource;
 
 /**
  * Test case for Highest Set Bit
@@ -39,9 +43,16 @@ public class OnesComplementTest {
         assertEquals("1001", OnesComplement.onesComplement("0110"));
     }
 
+    @ParameterizedTest
+    @NullAndEmptySource
+    public void testOnesComplementNullOrEmptyInputThrowsException(String input) {
+        IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> OnesComplement.onesComplement(input));
+        assertEquals("Input must be a non-empty binary string.", exception.getMessage());
+    }
+
     @Test
-    public void testOnesComplementEmptyString() {
-        // Test empty string scenario
-        assertEquals("", OnesComplement.onesComplement(""));
+    public void testOnesComplementInvalidCharactersThrowsException() {
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> OnesComplement.onesComplement("10a1"));
+        assertTrue(exception.getMessage().startsWith("Input must contain only '0' and '1'"));
     }
 }