Quality control describes the directed use of testing to measure the achievement of a specified standard. Quality control is a formal (as in structured, not as in wearing-a-tuxedo fancy) use of testing. Quality control is a superset of testing, although it often used synonymously with testing. Roughly, you test to see if something is broken, and with quality control you set limits that say, in effect, if this particular stuff is broken then whatever you're testing fails.
Yet another way of looking at the difference between testing and quality control is to consider the difference between a test as an event and a test as a part of a system. For example, let's say our test is the measurement of your ability to assemble a jigsaw puzzle in one hour. We test you today, and you complete the puzzle in fifty-eight minutes, so you pass. This seems pretty trivial, but say that there is some need in your life requiring you to solve puzzles quickly: we tested you once, but we must verify that you can meet this weird requirement continually over time. The solution is to test you at regular intervals, which will allow us to see if you can still be successful when under stress, when you haven't slept, when your workload is high -- our quality control approach to this issue says "you must finish puzzle in one hour or less" and "we will test this requirement periododically over time". And as a side effect of this quality control testing, you might find that you are more likely to improve in your puzzle solving skills because of the repeated practice; this is the beginning of a shift to quality
Yet another way of looking at the difference between testing and quality control is to consider the difference between a test as an event and a test as a part of a system. For example, let's say our test is the measurement of your ability to assemble a jigsaw puzzle in one hour. We test you today, and you complete the puzzle in fifty-eight minutes, so you pass. This seems pretty trivial, but say that there is some need in your life requiring you to solve puzzles quickly: we tested you once, but we must verify that you can meet this weird requirement continually over time. The solution is to test you at regular intervals, which will allow us to see if you can still be successful when under stress, when you haven't slept, when your workload is high -- our quality control approach to this issue says "you must finish puzzle in one hour or less" and "we will test this requirement periododically over time". And as a side effect of this quality control testing, you might find that you are more likely to improve in your puzzle solving skills because of the repeated practice; this is the beginning of a shift to quality
