How To Check If It's The Last Result And Remove Comma

I am wondering if anyone could help. I have a loop that displays my results and places a comma after each. The problem is that when the last result is displayed, it shows the comma.

Example:
for loop{
echo $row['test'].', ';

}

displays...  test1, test2, test3,

Notice after test3, there is still a comma? How do I remove it and have it display... test1, test2, test3