Using PHP, design a function that given a Roman numeral (Links to an external site.) in input, is able to compute the modern HinduArabic numeral (Links to an external site.) system representation (aka, 0123456789).

For example:

Input	Output
VI	6
IV	4
MCMXC	1990
IX	9

• Be sure to add all the necessary checks and at least one testing function.
• Try to split the logic in small functions.

What is a "check"? If you have a function that accepts an input, you want to check if such input falls in the right boundary or, in case of loosly typed languages such as PHP, if belongs to the right type.

Example:

function test(nr) { if (nr < 0) return NULL else { // the function can continue ... } }