String indexOf Lab

In this lab exercise, you will be working with the String.prototype.indexOf() method to find the index of a substring inside a given string. The indexOf() method returns the first index at which a given substring is found or -1 if it is not present.

Your task is to create a custom findSubstringIndex function that accepts two parameters (a text string and a substring to be found) and returns the index of the substring in the text using the indexOf method.

Keep in mind that the function should also check if the input strings are empty and return -1 if empty. Default export the function using ESM syntax for the test cases to verify your code