added test to test special case of input 0

test/conversionOfNumbers/test_conversionOfNumbers.c

@@ -165,3 +165,15 @@ void test_hexStringLengthOfInput255is2(){
     //assert
     TEST_ASSERT_EQUAL_INT(expected, result);
 }
+
+void test_hexStringLengthOfInput0is1(){
+    //arrange
+    int result;
+    int expected = 1;
+
+    //act
+    result = hexStrLen(0);
+
+    //assert
+    TEST_ASSERT_EQUAL_INT(expected, result);
+}