how can I invoke function between different project in one projectSuit?

Hi there,

    Here is my case,  There one projectSuit name TestSuite,  I created ProjectOne and ProjectTwo in it, Then created Unit1 in ProjectOne, created Unit1 in ProjectTwo, Is there anythy that I invoke a function of Unit1 in ProjectTwo from a function of Unit1 in ProjectOne?

    Thanks in adcanced。