You do not build such an interface. The interface's purpose is not to be tested, it is to provide abstraction to a solution. Unit tests greatest value is not ensuring that the solution is correct, but rather that the solution has coverage such that it can be modified without introducing new bugs. If you have proper coverage, the tests will identify new bugs immediately.

In reply to Re: How to build a testable interface? by Anonymous Monk
in thread How to build a testable interface? by McMahon

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