LNK2019
And what else does it say besides "LNK2019"? Probably something about can't find a CTester constructor or a CTester:: GetParam() method, right? So did you add "Tester.cpp" or whatever you called the source file to the project? Did you add the paths to and names of your Qt library ".lib" files to the link properties? (Qt5Core, Qt5Gui, and Qt5Widgets, at a minimum for a GUI project).

By the way, you -do- realize that the code in your line 3 does nothing, right? Gets the parameter value, doesn't assign it to anything, then throws it away once the statment is done.