How can I add a target goal for each individual column in a chart?

If you can get to the # of tests completed and # of tests remaining (the # required minus the # completed), in two different fields, you can show them both in a stacked bar chart. You could show the # completed in green, and the # remaining in red, or something along those lines. This way, it would be clear what the total is (the total height of the combined bars), and how close you are to reaching it.

I suppose you could also indicate an overage with a third field/stacked bar/color.

Hope this helps.