> ...trigger alarms when patient's vital signs met certain criteria set by doctor
Most of us aren't working on life or death code like this. My React app doesn't need 100% code coverage but you put it well when you said "There should be just enough to feel safe"
What I really want to drive home is that you should listen to the engineers who are working on the project. Testing is one of those things that is entirely subject to project needs. Like you say, a React app doesn't need 100% coverage, neither does code running a CI, something far out of the serving path, etc. But we shouldn't have a knee-jerk reaction to an engineer saying we should have 100% coverage.
Most of us aren't working on life or death code like this. My React app doesn't need 100% code coverage but you put it well when you said "There should be just enough to feel safe"