Re-installing minted fixed the issue. To uninstall a package in MikTex, go to Package Manager (Admin). Reinstall minted under TexMaker, after that I don't even need the \newcommand\TestAppExists[3]{#2}. Just make sure you add the scripts pygmentize.cmd to the C:\Python27\Scripts\ with the content:
@echo offset PYTHONPATH=C:\Python27%PYTHONPATH%\python.exe %PYTHONPATH%\Scripts\pygmentize %*Note: The one in the instruction document missed a \ after %PYTHON%. Further, this solution only works under Windows environment, for Linux variants, you have to go with Joseph Wright's solution.
