Decompose and Expose

Large, complex private methods are a code smell. An implementation which is so complex that it cannot be usefully decomposed into component parts (with public interfaces) is a problem in testability that reveals potential design and architectural problems. The 1% of cases where the private code is huge will usually benefit from rework to decompose and expose. – S.Lott Feb 14 '12 at 20:06

http://softwareengineering.stackexchange.com/questions/135047/new-to-tdd-should-i-avoid-private-methods-now#comment253312_135049