PokerEquityCalculator | poker equity calculator as montecarlo simulation | Frontend Framework library

Definitions of eval_best_hand and its dependencies are present only in EquityCalculatorMontecarlo project that is an executable, you are just referring the function declaration of eval_best_hand from header files in your Tests project but not linking them. Either you make the definitions of whatever functions designated to be used in other projects (Executables) into a common static lib (Say Utils.lib), and link your projects against that static library or include all the .cpp files that contains definitions of necessary functions to Tests.vcxproj.

I think, simply adding Scoring.cpp and Deck.cpp to Tests.vcxproj will solve the linker errors.

You may also create a separate project namely "Utils.lib" with only Scoring.cpp and Deck.cpp source files and link that lib to whatever executable project that needs to consume those utility methods. This is basically to meet the purpose of reusing and easy maintenance. In this case your main project (EquityCalculatorMontecarlo) may only contain a main function and code to consume functions in Scoring.h and Deck.h(Definitions present in Utils.lib).