OO vs Unit-testing

One reason for why unit testing has bothered me is that it goes against an OO principle I was thought at school, namely that every aspect of the code should be kept as private as possible.

Roy Osherove has a recent entry on this subject. Roy is an enthusiastic unit-tester, I am still in doubt :)

UPDATED 24.7.2007
Bruce Eckel's thoughts on OOP.

TDD presupposition

I am pondering the validity of the following statement:

"The theory is that testable code is better designed ... If the class is easier to test, it is a better design. The test first paradigm just forces you to use good design. It makes a good design the path of least resistance." -David Hogue

I know that this is taken as a given in unit-test camps, but is it?

UPDATED: 1.1.2008
I found out that I am not alone in not being convinced about designing for testability. The creator of TypeMock feels that designing for testability does not comply with YAGNI.