Add test case for HexaDecimalToBinary (TheAlgorithms#3683)

Author: naanagon

src/main/java/com/thealgorithms/conversions/HexaDecimalToBinary.java

@@ -5,13 +5,13 @@ public class HexaDecimalToBinary {
 
     private final int LONG_BITS = 8;
 
-    public void convert(String numHex) {
+    public String convert(String numHex) {
         // String a HexaDecimal:
         int conHex = Integer.parseInt(numHex, 16);
         // Hex a Binary:
         String binary = Integer.toBinaryString(conHex);
         // Output:
-        System.out.println(numHex + " = " + completeDigits(binary));
+        return completeDigits(binary);
     }
 
     public String completeDigits(String binNum) {
@@ -39,7 +39,7 @@ public static void main(String[] args) {
         HexaDecimalToBinary objConvert = new HexaDecimalToBinary();
 
         for (String num : hexNums) {
-            objConvert.convert(num);
+            System.out.println(num + " = " + objConvert.convert(num));
         }
     }
 }

src/test/java/com/thealgorithms/conversions/HexaDecimalToBinaryTest.java

@@ -0,0 +1,14 @@
+package com.thealgorithms.conversions;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class HexaDecimalToBinaryTest {
+
+    @Test
+    public void testHexaDecimalToBinary(){
+        HexaDecimalToBinary hexaDecimalToBinary = new HexaDecimalToBinary();
+        assertEquals("1111111111111111111111111111111", hexaDecimalToBinary.convert("7fffffff"));
+        assertEquals("101010111100110111101111", hexaDecimalToBinary.convert("abcdef"));
+    }
+}