Mode of operation, defaults to rethrow.
rethrow: If any errors are passed into the handler in tests, it typically means that there is a bug in the application or test, so this mock will
make these tests fail.
log: Sometimes it is desirable to test that an error is thrown, for this case the log mode stores an array of errors in `$exceptionHandler.errors`, to allow later assertion of them.
See <a href="api/ngMock.$log#assertEmpty">assertEmpty()</a> and
<a href="api/ngMock.$log#reset">reset()</a>