added test for converting into hex for numbers smaller than 16

test/conversionOfNumbers/test_conversionOfNumbers.c

@@ -128,3 +128,16 @@ void test_convert3ToHexStr3(){
     TEST_ASSERT_EQUAL_STRING(expected, result);
     free(result);
 }
+
+void test_convert12ToHexStrC(){
+    //arrange
+    char* result;
+    char expected[] = "C";
+
+    //act
+    result = convertIntToHex(12);
+
+    //assert
+    TEST_ASSERT_EQUAL_STRING(expected, result);
+    free(result);
+}