A "test" parameter for the msvc_build.bat

I'd greatly appreciate this as it would be a great way to prevent the issue I seem to be having where I make a PR and it turns out that my code breaks a bunch of tests, which then obviously can't be merged. Even if I fix it up, it's then preferred I "squash" my commits, which I didn't actually have a lot of luck with last time.

If I could test code before I create a PR, then I'd be able to commit everything within one commit. Unfortunately, I can't use mingw32-make as I get these errors for whatever reason:

C:\ProjectFiles\mscore\MuseScore>C:\MinGW\bin\mingw32-make -f Makefile.mingw debug
if not exist build.debug\nul mkdir build.debug
/usr/bin/sh: -c: line 1: syntax error: unexpected end of file
Makefile.mingw:37: recipe for target 'debug' failed
mingw32-make: *** [debug] Error 1

Please, I'd love to be able to do this through the msvc_build.bat script.