> A test validates that a method raises an exception when being fed a null is pointless if it’s just testing a one line assertion that does the same thing. It’s a waste of keystrokes. It doesnt catch bugs.

It catches the bug that gets created when someone does a later refactor, replaces the assertion and some other code with a call to another function that they think throws an exception on null as well as doing some computation needed in the current function, but they are wrong.

Tests validating the contract of the unit are useful even when the trivially pass in the first-pass implementation, because implementations evolve, and the thing people will forget to add tests for with changes are the pre-existing, unmodified expected behavior.

(Also, for workflows where tests are written before the first-pass implementation.)