Enhance docs, remove main. add more tests in `HexaDecimal… (#5923)

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

@@ -1,14 +1,37 @@
 package com.thealgorithms.conversions;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
-import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 public class HexaDecimalToDecimalTest {
 
-    @Test
-    public void testhexaDecimalToDecimal() {
-        assertEquals(161, HexaDecimalToDecimal.getHexaToDec("A1"));
-        assertEquals(428, HexaDecimalToDecimal.getHexaToDec("1ac"));
+    @ParameterizedTest
+    @CsvSource({
+        "A1, 161", // Simple case with two characters
+        "1AC, 428", // Mixed-case input
+        "0, 0", // Single zero
+        "F, 15", // Single digit
+        "10, 16", // Power of 16
+        "FFFF, 65535", // Max 4-character hex
+        "7FFFFFFF, 2147483647" // Max positive int value
+    })
+    public void
+    testValidHexaToDecimal(String hexInput, int expectedDecimal) {
+        assertEquals(expectedDecimal, HexaDecimalToDecimal.getHexaToDec(hexInput));
+    }
+
+    @ParameterizedTest
+    @CsvSource({
+        "G", // Invalid character
+        "1Z", // Mixed invalid input
+        "123G", // Valid prefix with invalid character
+        "#$%" // Non-hexadecimal symbols
+    })
+    public void
+    testInvalidHexaToDecimal(String invalidHex) {
+        assertThrows(IllegalArgumentException.class, () -> HexaDecimalToDecimal.getHexaToDec(invalidHex));
     }
 }