Changeset 48937 for trunk

Tests: First pass at using assertSame() instead of assertEquals() in most of the unit tests.

This ensures that not only the return values match the expected results, but also that their type is the same.

Going forward, stricter type checking by using assertSame() should generally be preferred to assertEquals() where appropriate, to make the tests more reliable.

Props johnbillion, jrf, SergeyBiryukov.
See #38266.