[serial_dev]

This sounds like the good old "having high test coverage is bad because I can get to 100% just by calling functions and doing nothing, asserting nothing with them".

100% test coverage doesn't mean your tests are good, but having 50% (or pick your number) means they are bad / not sufficient.

[heavenlyblue]

That isn't even necessarily true. For interpreted languages having a test that just runs code asserts that the code is able to run (i.e. you are not calling a string object as a function for example). Which is not enough to always assert functionality but still better than nothing.

[HPsquared]

In other words it's "necessary, but not sufficient".