I'm curious to know exactly what the science is behind the tests being performed currently. And how does a body typically fight a virus in the first place? Th

I'm curious to know exactly what the science is behind the tests being performed currently. And how does a body typically fight a virus in the first place? This might sound amateurish (it is), but I have been picturing this virus and how our bodies are fighting it similar to how our bodies fight cancer. Tons of people who never end up with cancer diagnosis are constantly fighting off cancer cells, it's just that the capacity of their (relatively) healthy bodies exceeds the total # of cancer cells they need to fight off. Is it possible these tests have become too sensitive to where they're easily detecting the virus in seemingly healthy people?