If you're enjoying your lens, does it matter if it's front focusing? Keep in mind that practically all lenses front/back focus to a certain degree which is why all modern cameras have AF micro adjustment. It's not unusual to have to adjust your focus on professional L series lenses.
Anyway, the way to determine if there are focusing issues is to do the following (Note: You'll need a tripod and a camera capable of live view):
1) Pick a suitable target. Preferably flat, with good contrasts. Newspaper prints stuck onto the wall is a good example.
2) Line up your with the target. Ensure that your lens is perpendicular (i.e. at 90 degrees) to your target in both horizontal and vertical axis.
3) Make sure you're at a sensible distance from the target. Best to pick a distance you'll normally work at (for this lens I chose 4m). This step is a little tricky as there are others who suggest going for 15x - 20x the focus length. So if you're testing at 70mm, you'll want to make sure you're 10.5m - 14m away from the target. This isn't always practical, and I don't normally shoot objects that far away.
4) Switch on live view and focus on the target. Zoom in to max on live view, this should bring up the point of focus into view. Now turn the focus ring so that it focuses away from you. If the image became sharper, you've got front focus. If you turn the focus ring so that the focus comes towards you and the image becomes sharper, you've got backfocus.