Mocking a final method from a base class on a class extending it fails silently

[pzaj2]

Q	A
PHPUnit version	7.3.5
PHP version	7.2.9
Installation Method	Composer

Simply put, mocking a class extending \Exception I was wondering why getMessage returns an empty string despite being mocked. It happens to be a public final method of \Exception. While I haven't checked, I'd risk saying that this will happen for other classes with final methods being extended.

Expected behaviour:
Issue / display a warning saying this method cannot be mocked / stubbed.

Actual behaviour:
The method is not mocked, it works as it would normally (in this case returning an empty string).

[sebastianbergmann]

Duplicate of #3127.