The title is disingenuous. A better title would be "100% test coverage should be the goal". Though that is laughably obvious and would generate no clicks, so I can see why the author made the choice they did.

That said, if you have a single test, that better than no tests. And 90% is better than 80%. Yes, 100% is ideal, but if you let perfect be the enemy of good, than you waste time when low hanging fruit breaks.