Had under tested, the rate of testing has increased drastically in the last two weeks. It’s not where we need it to be, but the US is now testing at a rate comparable with any other country.
The reason Britain has an extreme 8% mortality rate on its positive cases, is because they aren't testing properly (and haven't been). They'd already be at 100,000+ cases if they were testing just at the rate the US is. France as another example has such an extreme case mortality rate (7%) in part because they're not testing enough people. Their positive result would be far higher than ~60k right now if they were (and that mortality rate would drop considerably).
One of the reasons Germany's mortality rate is so low, is they're catching a very large number of all positive cases via massive testing. If the US were testing at the rate of Germany, its case mortality rate (which is around 2.3%) would drop by more than 1/2.
This site has done a very good job at bringing together all the available testing data across the states.
> If your symptoms are mild, you should stay at home and monitor your condition. Testing is only offered to patients who are severely ill and need hospitalization.