Well as for refusing testing. It's been a thing in Japan for a while now. In fact, Japan never really did get into doing a lot of tests from the get go. There's been a bit over ~8000 tests to date I think (on a multi million population, that's nothing).
Sweden, my home country, is doing the same thing. Tests are not being done to the extent that people want them to be done.
I can't help but think this is an intentional strategy to keep people from panicking. If the official numbers are low people and media alike has to refer to those. "we only have x cases so far, no need for panic". And people with mild symptoms (unaware they're infected) will still have to go to work and society and the economy will take less damage.
If you tested EVERYONE, many countries would most likely end up like Italy or worse, because the hospitals would be swamped. People would have to stay home at an alarming rate and things would just... stop working.
But any sensible person should realize that the virus is spreading like crazy. Official numbers, just throw them out the window. How many is really infected is anyone's guess. We'll never know since testing isn't being done.
The 1.5 million city I live in has something like 3 confirmed cases in total.... yeah right. It's a tourist destination and we had a lot of Chinese tourists (still have?) this season. I'd put 3, maybe four zeros after that official number if I were to estimate. And I wouldn't be surprised if it was even more.
As for buying up food and stuff in panic. It's a bit dumb, BUT, you have to realize that when people are panicking the ones who do not go and buy themselves some toilet paper and food are the ones who's going to be suffering.
I don't think it's fair to say everyone is panicking and acting dumb, buying a lot of stuff at the super markets and what not. Some are for sure, but I think the vast majority is simply acting rationally on the situation.
I can see two good reasons to buy a small stock of supplies if you're able to:
1) If you go once to the super market and buy some surplus of whatever you need, then you can self quarantine and AVOID going to the super market every other day which will significantly lower the risk of infection and spread. This is good.
2) You realize that a lot of people are buying up stuff right now all over the world and that if the stores run out of essential goods you want or need, you don't know when next you'll be able to buy them. So you hurry down and buy some surplus. This is not really bad either, unless you go way overboard.
I went down and bought a reasonable amount of "stuff" as soon as I could. My reasoning for doing so was a combination of number "1" and "2".
In my case, reasonable amount was about ~2, maybe 3 weeks of supplies. As well as one backup of each household item such as soap and toothpaste since I don't want to be surprised and forced to go down to the supermarket anyway when they run out. Wouldn't really call that going overboard at all.
If you don't feel it's necessary where you live, that's fine. Maybe it isn't. I just don't want to be caught with my pants down (without toilet paper).
Reasonable precaution and preparedness is best.