You shouldn't have to... or want to test that often.
Keep in mind, it takes bandwidth to test bandwidth. While you're testing, ideally you suck up ALL of your available bandwidth. If you're testing too often you'd be degrading your own networks.
When you do 5 minute auto test intervals you should only do so for short periods. Otherwise the test is counter productive to the faster, smoother more reliable Internet everyone is trying to accomplish here.
Addition:
Having said that... I have some special things I'm working on that have test intervals in seconds and require almost no bandwidth.
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