Find indexnumber of substring in string

Hi,

I would like to have a macro that searches the index number of "test" in a cell A2. For example if the string in cell A2 is 111test11 than B2 should display 4. How can i do this?

I made this function but it doesn't work:

c.Offset(, 1).Value = InStr(1, Range("a2").Value, "test")

Any input is much appreciated!